/src/git/reftable/stack.c

Source
/*
 * Copyright 2020 Google LLC
 *
 * Use of this source code is governed by a BSD-style
 * license that can be found in the LICENSE file or at
 * https://developers.google.com/open-source/licenses/bsd
 */

#include "stack.h"

#include "system.h"
#include "constants.h"
#include "merged.h"
#include "reftable-error.h"
#include "reftable-record.h"
#include "reftable-merged.h"
#include "table.h"
#include "writer.h"

static int stack_filename(struct reftable_buf *dest, struct reftable_stack *st,
        const char *name)
{
  int err;
  reftable_buf_reset(dest);
  if ((err = reftable_buf_addstr(dest, st->reftable_dir)) < 0 ||
      (err = reftable_buf_addstr(dest, "/")) < 0 ||
      (err = reftable_buf_addstr(dest, name)) < 0)
    return err;
  return 0;
}

static ssize_t reftable_write_data(int fd, const void *data, size_t size)
{
  size_t total_written = 0;
  const char *p = data;

  while (total_written < size) {
    ssize_t bytes_written = write(fd, p, size - total_written);
    if (bytes_written < 0 && (errno == EAGAIN || errno == EINTR))
      continue;
    if (bytes_written < 0)
      return REFTABLE_IO_ERROR;

    total_written += bytes_written;
    p += bytes_written;
  }

  return total_written;
}

struct fd_writer {
  const struct reftable_write_options *opts;
  int fd;
};

static ssize_t fd_writer_write(void *arg, const void *data, size_t sz)
{
  struct fd_writer *writer = arg;
  return reftable_write_data(writer->fd, data, sz);
}

static int fd_writer_flush(void *arg)
{
  struct fd_writer *writer = arg;
  return fsync(writer->fd);
}

static int fd_read_lines(int fd, char ***namesp)
{
  char *buf = NULL;
  int err = 0;
  off_t size;

  size = lseek(fd, 0, SEEK_END);
  if (size < 0) {
    err = REFTABLE_IO_ERROR;
    goto done;
  }

  err = lseek(fd, 0, SEEK_SET);
  if (err < 0) {
    err = REFTABLE_IO_ERROR;
    goto done;
  }

  REFTABLE_ALLOC_ARRAY(buf, size + 1);
  if (!buf) {
    err = REFTABLE_OUT_OF_MEMORY_ERROR;
    goto done;
  }

  for (off_t total_read = 0; total_read < size; ) {
    ssize_t bytes_read = read(fd, buf + total_read, size - total_read);
    if (bytes_read < 0 && (errno == EAGAIN || errno == EINTR))
      continue;
    if (bytes_read < 0 || !bytes_read) {
      err = REFTABLE_IO_ERROR;
      goto done;
    }

    total_read += bytes_read;
  }
  buf[size] = 0;

  err = parse_names(buf, size, namesp);
done:
  reftable_free(buf);
  return err;
}

int read_lines(const char *filename, char ***namesp)
{
  int fd = open(filename, O_RDONLY);
  int err = 0;
  if (fd < 0) {
    if (errno == ENOENT) {
      REFTABLE_CALLOC_ARRAY(*namesp, 1);
      if (!*namesp)
        return REFTABLE_OUT_OF_MEMORY_ERROR;
      return 0;
    }

    return REFTABLE_IO_ERROR;
  }
  err = fd_read_lines(fd, namesp);
  close(fd);
  return err;
}

int reftable_stack_init_ref_iterator(struct reftable_stack *st,
              struct reftable_iterator *it)
{
  return merged_table_init_iter(reftable_stack_merged_table(st),
              it, REFTABLE_BLOCK_TYPE_REF);
}

int reftable_stack_init_log_iterator(struct reftable_stack *st,
             struct reftable_iterator *it)
{
  return merged_table_init_iter(reftable_stack_merged_table(st),
              it, REFTABLE_BLOCK_TYPE_LOG);
}

struct reftable_merged_table *
reftable_stack_merged_table(struct reftable_stack *st)
{
  return st->merged;
}

static int has_name(char **names, const char *name)
{
  while (*names) {
    if (!strcmp(*names, name))
      return 1;
    names++;
  }
  return 0;
}

/* Close and free the stack */
void reftable_stack_destroy(struct reftable_stack *st)
{
  char **names = NULL;
  int err = 0;

  if (!st)
    return;

  if (st->merged) {
    reftable_merged_table_free(st->merged);
    st->merged = NULL;
  }

  if (st->list_file)
    err = read_lines(st->list_file, &names);
  if (err < 0) {
    REFTABLE_FREE_AND_NULL(names);
  }

  if (st->tables) {
    struct reftable_buf filename = REFTABLE_BUF_INIT;

    for (size_t i = 0; i < st->tables_len; i++) {
      const char *name = reftable_table_name(st->tables[i]);
      int try_unlinking = 1;

      reftable_buf_reset(&filename);
      if (names && !has_name(names, name)) {
        if (stack_filename(&filename, st, name) < 0)
          try_unlinking = 0;
      }
      reftable_table_decref(st->tables[i]);

      if (try_unlinking && filename.len) {
        /* On Windows, can only unlink after closing. */
        unlink(filename.buf);
      }
    }

    reftable_buf_release(&filename);
    st->tables_len = 0;
    REFTABLE_FREE_AND_NULL(st->tables);
  }

  if (st->list_fd >= 0) {
    close(st->list_fd);
    st->list_fd = -1;
  }

  REFTABLE_FREE_AND_NULL(st->list_file);
  REFTABLE_FREE_AND_NULL(st->reftable_dir);
  reftable_free(st);
  free_names(names);
}

static struct reftable_table **stack_copy_tables(struct reftable_stack *st,
             size_t cur_len)
{
  struct reftable_table **cur = reftable_calloc(cur_len, sizeof(*cur));
  if (!cur)
    return NULL;
  for (size_t i = 0; i < cur_len; i++)
    cur[i] = st->tables[i];
  return cur;
}

static int reftable_stack_reload_once(struct reftable_stack *st,
              const char **names,
              int reuse_open)
{
  size_t cur_len = !st->merged ? 0 : st->merged->tables_len;
  struct reftable_table **cur = NULL;
  struct reftable_table **reused = NULL;
  struct reftable_table **new_tables = NULL;
  size_t reused_len = 0, reused_alloc = 0, names_len;
  size_t new_tables_len = 0;
  struct reftable_merged_table *new_merged = NULL;
  struct reftable_buf table_path = REFTABLE_BUF_INIT;
  int err = 0;
  size_t i;

  if (cur_len) {
    cur = stack_copy_tables(st, cur_len);
    if (!cur) {
      err = REFTABLE_OUT_OF_MEMORY_ERROR;
      goto done;
    }
  }

  names_len = names_length(names);

  if (names_len) {
    new_tables = reftable_calloc(names_len, sizeof(*new_tables));
    if (!new_tables) {
      err = REFTABLE_OUT_OF_MEMORY_ERROR;
      goto done;
    }
  }

  while (*names) {
    struct reftable_table *table = NULL;
    const char *name = *names++;

    /* this is linear; we assume compaction keeps the number of
       tables under control so this is not quadratic. */
    for (i = 0; reuse_open && i < cur_len; i++) {
      if (cur[i] && 0 == strcmp(cur[i]->name, name)) {
        table = cur[i];
        cur[i] = NULL;

        /*
         * When reloading the stack fails, we end up
         * releasing all new tables. This also
         * includes the reused tables, even though
         * they are still in used by the old stack. We
         * thus need to keep them alive here, which we
         * do by bumping their refcount.
         */
        REFTABLE_ALLOC_GROW_OR_NULL(reused,
                  reused_len + 1,
                  reused_alloc);
        if (!reused) {
          err = REFTABLE_OUT_OF_MEMORY_ERROR;
          goto done;
        }
        reused[reused_len++] = table;
        reftable_table_incref(table);
        break;
      }
    }

    if (!table) {
      struct reftable_block_source src = { NULL };

      err = stack_filename(&table_path, st, name);
      if (err < 0)
        goto done;

      err = reftable_block_source_from_file(&src,
                    table_path.buf);
      if (err < 0)
        goto done;

      err = reftable_table_new(&table, &src, name);
      if (err < 0)
        goto done;
    }

    new_tables[new_tables_len] = table;
    new_tables_len++;
  }

  /* success! */
  err = reftable_merged_table_new(&new_merged, new_tables,
          new_tables_len, st->opts.hash_id);
  if (err < 0)
    goto done;

  /*
   * Close the old, non-reused tables and proactively try to unlink
   * them. This is done for systems like Windows, where the underlying
   * file of such an open table wouldn't have been possible to be
   * unlinked by the compacting process.
   */
  for (i = 0; i < cur_len; i++) {
    if (cur[i]) {
      const char *name = reftable_table_name(cur[i]);

      err = stack_filename(&table_path, st, name);
      if (err < 0)
        goto done;

      reftable_table_decref(cur[i]);
      unlink(table_path.buf);
    }
  }

  /* Update the stack to point to the new tables. */
  if (st->merged)
    reftable_merged_table_free(st->merged);
  new_merged->suppress_deletions = st->opts.suppress_deletions;
  st->merged = new_merged;

  if (st->tables)
    reftable_free(st->tables);
  st->tables = new_tables;
  st->tables_len = new_tables_len;
  new_tables = NULL;
  new_tables_len = 0;

  /*
   * Decrement the refcount of reused tables again. This only needs to
   * happen on the successful case, because on the unsuccessful one we
   * decrement their refcount via `new_tables`.
   */
  for (i = 0; i < reused_len; i++)
    reftable_table_decref(reused[i]);

done:
  for (i = 0; i < new_tables_len; i++)
    reftable_table_decref(new_tables[i]);
  reftable_free(new_tables);
  reftable_free(reused);
  reftable_free(cur);
  reftable_buf_release(&table_path);
  return err;
}

static int reftable_stack_reload_maybe_reuse(struct reftable_stack *st,
               int reuse_open)
{
  char **names = NULL, **names_after = NULL;
  uint64_t deadline;
  int64_t delay = 0;
  int tries = 0, err;
  int fd = -1;

  deadline = reftable_time_ms() + 3000;

  while (1) {
    uint64_t now = reftable_time_ms();

    /*
     * Only look at deadlines after the first few times. This
     * simplifies debugging in GDB.
     */
    tries++;
    if (tries > 3 && now >= deadline)
      goto out;

    fd = open(st->list_file, O_RDONLY);
    if (fd < 0) {
      if (errno != ENOENT) {
        err = REFTABLE_IO_ERROR;
        goto out;
      }

      REFTABLE_CALLOC_ARRAY(names, 1);
      if (!names) {
        err = REFTABLE_OUT_OF_MEMORY_ERROR;
        goto out;
      }
    } else {
      err = fd_read_lines(fd, &names);
      if (err < 0)
        goto out;
    }

    err = reftable_stack_reload_once(st, (const char **) names, reuse_open);
    if (!err)
      break;
    if (err != REFTABLE_NOT_EXIST_ERROR)
      goto out;

    /*
     * REFTABLE_NOT_EXIST_ERROR can be caused by a concurrent
     * writer. Check if there was one by checking if the name list
     * changed.
     */
    err = read_lines(st->list_file, &names_after);
    if (err < 0)
      goto out;
    if (names_equal((const char **) names_after,
        (const char **) names)) {
      err = REFTABLE_NOT_EXIST_ERROR;
      goto out;
    }

    free_names(names);
    names = NULL;
    free_names(names_after);
    names_after = NULL;
    close(fd);
    fd = -1;

    delay = delay + (delay * reftable_rand()) / UINT32_MAX + 1;
    poll(NULL, 0, delay);
  }

out:
  /*
   * Invalidate the stat cache. It is sufficient to only close the file
   * descriptor and keep the cached stat info because we never use the
   * latter when the former is negative.
   */
  if (st->list_fd >= 0) {
    close(st->list_fd);
    st->list_fd = -1;
  }

  /*
   * Cache stat information in case it provides a useful signal to us.
   * According to POSIX, "The st_ino and st_dev fields taken together
   * uniquely identify the file within the system." That being said,
   * Windows is not POSIX compliant and we do not have these fields
   * available. So the information we have there is insufficient to
   * determine whether two file descriptors point to the same file.
   *
   * While we could fall back to using other signals like the file's
   * mtime, those are not sufficient to avoid races. We thus refrain from
   * using the stat cache on such systems and fall back to the secondary
   * caching mechanism, which is to check whether contents of the file
   * have changed.
   *
   * On other systems which are POSIX compliant we must keep the file
   * descriptor open. This is to avoid a race condition where two
   * processes access the reftable stack at the same point in time:
   *
   *   1. A reads the reftable stack and caches its stat info.
   *
   *   2. B updates the stack, appending a new table to "tables.list".
   *      This will both use a new inode and result in a different file
   *      size, thus invalidating A's cache in theory.
   *
   *   3. B decides to auto-compact the stack and merges two tables. The
   *      file size now matches what A has cached again. Furthermore, the
   *      filesystem may decide to recycle the inode number of the file
   *      we have replaced in (2) because it is not in use anymore.
   *
   *   4. A reloads the reftable stack. Neither the inode number nor the
   *      file size changed. If the timestamps did not change either then
   *      we think the cached copy of our stack is up-to-date.
   *
   * By keeping the file descriptor open the inode number cannot be
   * recycled, mitigating the race.
   */
  if (!err && fd >= 0 && !fstat(fd, &st->list_st) &&
      st->list_st.st_dev && st->list_st.st_ino) {
    st->list_fd = fd;
    fd = -1;
  }

  if (fd >= 0)
    close(fd);
  free_names(names);
  free_names(names_after);

  if (st->opts.on_reload)
    st->opts.on_reload(st->opts.on_reload_payload);

  return err;
}

int reftable_new_stack(struct reftable_stack **dest, const char *dir,
           const struct reftable_stack_options *_opts)
{
  struct reftable_buf list_file_name = REFTABLE_BUF_INIT;
  struct reftable_stack_options opts = { 0 };
  struct reftable_stack *p;
  int err;

  p = reftable_calloc(1, sizeof(*p));
  if (!p) {
    err = REFTABLE_OUT_OF_MEMORY_ERROR;
    goto out;
  }

  if (_opts)
    opts = *_opts;
  if (opts.hash_id == 0)
    opts.hash_id = REFTABLE_HASH_SHA1;

  *dest = NULL;

  reftable_buf_reset(&list_file_name);
  if ((err = reftable_buf_addstr(&list_file_name, dir)) < 0 ||
      (err = reftable_buf_addstr(&list_file_name, "/tables.list")) < 0)
    goto out;

  p->list_file = reftable_buf_detach(&list_file_name);
  p->list_fd = -1;
  p->opts = opts;
  p->reftable_dir = reftable_strdup(dir);
  if (!p->reftable_dir) {
    err = REFTABLE_OUT_OF_MEMORY_ERROR;
    goto out;
  }

  p->list_lock = REFTABLE_FLOCK_INIT;

  err = reftable_stack_reload_maybe_reuse(p, 1);
  if (err < 0)
    goto out;

  *dest = p;
  err = 0;

out:
  if (err < 0)
    reftable_stack_destroy(p);
  return err;
}

/*
 * Check whether the given stack is up-to-date with what we have in memory.
 * If skip_if_locked is set skip stack reloading if the stack is currently
 * locked. Stack reloading must _not_ be skipped right after obtaining the
 * lock, to check for concurrent updates which may have happened.
 *
 * Returns 0 if so, 1 if the stack is out-of-date or a negative error code
 * otherwise.
 */
static int stack_uptodate(struct reftable_stack *st, int skip_if_locked)
{
  char **names = NULL;
  int err;

  if (skip_if_locked && st->list_lock.fd != -1)
    return 0;

  /*
   * When we have cached stat information available then we use it to
   * verify whether the file has been rewritten.
   *
   * Note that we explicitly do not want to use `stat_validity_check()`
   * and friends here because they may end up not comparing the `st_dev`
   * and `st_ino` fields. These functions thus cannot guarantee that we
   * indeed still have the same file.
   */
  if (st->list_fd >= 0) {
    struct stat list_st;

    if (stat(st->list_file, &list_st) < 0) {
      /*
       * It's fine for "tables.list" to not exist. In that
       * case, we have to refresh when the loaded stack has
       * any tables.
       */
      if (errno == ENOENT)
        return !!st->tables_len;
      return REFTABLE_IO_ERROR;
    }

    /*
     * When "tables.list" refers to the same file we can assume
     * that it didn't change. This is because we always use
     * rename(3P) to update the file and never write to it
     * directly.
     */
    if (st->list_st.st_dev == list_st.st_dev &&
        st->list_st.st_ino == list_st.st_ino)
      return 0;
  }

  err = read_lines(st->list_file, &names);
  if (err < 0)
    return err;

  for (size_t i = 0; i < st->tables_len; i++) {
    if (!names[i]) {
      err = 1;
      goto done;
    }

    if (strcmp(st->tables[i]->name, names[i])) {
      err = 1;
      goto done;
    }
  }

  if (names[st->merged->tables_len]) {
    err = 1;
    goto done;
  }

done:
  free_names(names);
  return err;
}

int reftable_stack_reload(struct reftable_stack *st)
{
  int err = stack_uptodate(st, 1);
  if (err > 0)
    return reftable_stack_reload_maybe_reuse(st, 1);
  return err;
}

struct reftable_addition {
  struct reftable_stack *stack;
  struct reftable_write_options opts;

  /*
   * While the list lock is acquired on the stack, we need to distinguish
   * which 'reftable_addition' is responsible for the lock. This avoids
   * clearing the lock of another 'reftable_addition'.
   */
  unsigned int locked : 1;

  char **new_tables;
  size_t new_tables_len, new_tables_cap;
  uint64_t next_update_index;
};

static void reftable_addition_close(struct reftable_addition *add)
{
  struct reftable_buf nm = REFTABLE_BUF_INIT;
  size_t i;

  for (i = 0; i < add->new_tables_len; i++) {
    if (!stack_filename(&nm, add->stack, add->new_tables[i]))
      unlink(nm.buf);
    reftable_free(add->new_tables[i]);
    add->new_tables[i] = NULL;
  }
  reftable_free(add->new_tables);
  add->new_tables = NULL;
  add->new_tables_len = 0;
  add->new_tables_cap = 0;

  if (add->locked)
    flock_release(&add->stack->list_lock);
  add->locked = 0;
  reftable_buf_release(&nm);
}

static int reftable_stack_init_addition(struct reftable_addition *add,
          struct reftable_stack *st,
          const struct reftable_write_options *opts)
{
  struct reftable_buf lock_file_name = REFTABLE_BUF_INIT;
  int err;

  memset(add, 0, sizeof(*add));
  add->stack = st;
  if (opts)
    add->opts = *opts;

  err = flock_acquire(&add->stack->list_lock, st->list_file,
          add->opts.lock_timeout_ms);
  if (err < 0)
    goto done;
  add->locked = 1;

  if (add->opts.default_permissions) {
    if (chmod(add->stack->list_lock.path,
        add->opts.default_permissions) < 0) {
      err = REFTABLE_IO_ERROR;
      goto done;
    }
  }

  err = stack_uptodate(st, 0);
  if (err < 0)
    goto done;
  if (err > 0) {
    err = reftable_stack_reload_maybe_reuse(add->stack, 1);
    if (err)
      goto done;
  }

  add->next_update_index = reftable_stack_next_update_index(st);
done:
  if (err)
    reftable_addition_close(add);
  reftable_buf_release(&lock_file_name);
  return err;
}

static int stack_try_add(struct reftable_stack *st,
       int (*write_table)(struct reftable_writer *wr,
              void *arg),
       void *arg,
       const struct reftable_write_options *opts)
{
  struct reftable_addition add;
  int err;

  err = reftable_stack_init_addition(&add, st, opts);
  if (err < 0)
    goto done;

  err = reftable_addition_add(&add, write_table, arg);
  if (err < 0)
    goto done;

  err = reftable_addition_commit(&add);
done:
  reftable_addition_close(&add);
  return err;
}

int reftable_stack_add(struct reftable_stack *st,
           int (*write)(struct reftable_writer *wr, void *arg),
           void *arg,
           const struct reftable_write_options *opts)
{
  int err = stack_try_add(st, write, arg, opts);
  if (err < 0) {
    return err;
  }

  return 0;
}

static int format_name(struct reftable_buf *dest, uint64_t min, uint64_t max)
{
  char buf[100];
  uint32_t rnd = reftable_rand();
  snprintf(buf, sizeof(buf), "0x%012" PRIx64 "-0x%012" PRIx64 "-%08x",
     min, max, rnd);
  reftable_buf_reset(dest);
  return reftable_buf_addstr(dest, buf);
}

void reftable_addition_destroy(struct reftable_addition *add)
{
  if (!add) {
    return;
  }
  reftable_addition_close(add);
  reftable_free(add);
}

int reftable_addition_commit(struct reftable_addition *add)
{
  struct reftable_buf table_list = REFTABLE_BUF_INIT;
  int err = 0;
  size_t i;

  if (add->new_tables_len == 0)
    goto done;

  for (i = 0; i < add->stack->merged->tables_len; i++) {
    if ((err = reftable_buf_addstr(&table_list, add->stack->tables[i]->name)) < 0 ||
        (err = reftable_buf_addstr(&table_list, "\n")) < 0)
      goto done;
  }
  for (i = 0; i < add->new_tables_len; i++) {
    if ((err = reftable_buf_addstr(&table_list, add->new_tables[i])) < 0 ||
        (err = reftable_buf_addstr(&table_list, "\n")) < 0)
      goto done;
  }

  err = reftable_write_data(add->stack->list_lock.fd,
          table_list.buf, table_list.len);
  reftable_buf_release(&table_list);
  if (err < 0) {
    err = REFTABLE_IO_ERROR;
    goto done;
  }

  err = fsync(add->stack->list_lock.fd);
  if (err < 0) {
    err = REFTABLE_IO_ERROR;
    goto done;
  }

  err = flock_commit(&add->stack->list_lock);
  if (err < 0) {
    err = REFTABLE_IO_ERROR;
    goto done;
  }
  add->locked = 0;

  /* success, no more state to clean up. */
  for (i = 0; i < add->new_tables_len; i++)
    reftable_free(add->new_tables[i]);
  reftable_free(add->new_tables);
  add->new_tables = NULL;
  add->new_tables_len = 0;
  add->new_tables_cap = 0;

  err = reftable_stack_reload_maybe_reuse(add->stack, 1);
  if (err)
    goto done;

  if (!add->opts.disable_auto_compact) {
    /*
     * Auto-compact the stack to keep the number of tables in
     * control. It is possible that a concurrent writer is already
     * trying to compact parts of the stack, which would lead to a
     * `REFTABLE_LOCK_ERROR` because parts of the stack are locked
     * already. Similarly, the stack may have been rewritten by a
     * concurrent writer, which causes `REFTABLE_OUTDATED_ERROR`.
     * Both of these errors are benign, so we simply ignore them.
     */
    err = reftable_stack_auto_compact(add->stack, &add->opts);
    if (err < 0 && err != REFTABLE_LOCK_ERROR &&
        err != REFTABLE_OUTDATED_ERROR)
      goto done;
    err = 0;
  }

done:
  reftable_addition_close(add);
  return err;
}

int reftable_stack_addition_new(struct reftable_addition **dest,
        struct reftable_stack *st,
        const struct reftable_write_options *opts)
{
  int err;

  REFTABLE_CALLOC_ARRAY(*dest, 1);
  if (!*dest)
    return REFTABLE_OUT_OF_MEMORY_ERROR;

  err = reftable_stack_init_addition(*dest, st, opts);
  if (err) {
    reftable_free(*dest);
    *dest = NULL;
  }

  return err;
}

int reftable_addition_add(struct reftable_addition *add,
        int (*write_table)(struct reftable_writer *wr,
               void *arg),
        void *arg)
{
  struct reftable_buf temp_tab_file_name = REFTABLE_BUF_INIT;
  struct reftable_buf tab_file_name = REFTABLE_BUF_INIT;
  struct reftable_buf next_name = REFTABLE_BUF_INIT;
  struct reftable_writer *wr = NULL;
  struct reftable_tmpfile tab_file = REFTABLE_TMPFILE_INIT;
  struct fd_writer writer = {
    .opts = &add->opts,
  };
  int err = 0;

  reftable_buf_reset(&next_name);

  err = format_name(&next_name, add->next_update_index, add->next_update_index);
  if (err < 0)
    goto done;

  err = stack_filename(&temp_tab_file_name, add->stack, next_name.buf);
  if (err < 0)
    goto done;

  err = reftable_buf_addstr(&temp_tab_file_name, ".temp.XXXXXX");
  if (err < 0)
    goto done;

  err = tmpfile_from_pattern(&tab_file, temp_tab_file_name.buf);
  if (err < 0)
    goto done;
  if (add->opts.default_permissions) {
    if (chmod(tab_file.path,
        add->opts.default_permissions)) {
      err = REFTABLE_IO_ERROR;
      goto done;
    }
  }

  writer.fd = tab_file.fd;
  err = reftable_writer_new(&wr, fd_writer_write, fd_writer_flush,
          &writer, add->stack->opts.hash_id, &add->opts);
  if (err < 0)
    goto done;

  err = write_table(wr, arg);
  if (err < 0)
    goto done;

  err = reftable_writer_close(wr);
  if (err == REFTABLE_EMPTY_TABLE_ERROR) {
    err = 0;
    goto done;
  }
  if (err < 0)
    goto done;

  err = tmpfile_close(&tab_file);
  if (err < 0)
    goto done;

  if (wr->min_update_index < add->next_update_index) {
    err = REFTABLE_API_ERROR;
    goto done;
  }

  err = format_name(&next_name, wr->min_update_index, wr->max_update_index);
  if (err < 0)
    goto done;

  err = reftable_buf_addstr(&next_name, ".ref");
  if (err < 0)
    goto done;

  err = stack_filename(&tab_file_name, add->stack, next_name.buf);
  if (err < 0)
    goto done;

  /*
    On windows, this relies on rand() picking a unique destination name.
    Maybe we should do retry loop as well?
   */
  err = tmpfile_rename(&tab_file, tab_file_name.buf);
  if (err < 0)
    goto done;

  REFTABLE_ALLOC_GROW_OR_NULL(add->new_tables, add->new_tables_len + 1,
            add->new_tables_cap);
  if (!add->new_tables) {
    err = REFTABLE_OUT_OF_MEMORY_ERROR;
    goto done;
  }
  add->new_tables[add->new_tables_len++] = reftable_buf_detach(&next_name);

done:
  tmpfile_delete(&tab_file);
  reftable_buf_release(&temp_tab_file_name);
  reftable_buf_release(&tab_file_name);
  reftable_buf_release(&next_name);
  reftable_writer_free(wr);
  return err;
}

uint64_t reftable_stack_next_update_index(struct reftable_stack *st)
{
  int sz = st->merged->tables_len;
  if (sz > 0)
    return reftable_table_max_update_index(st->tables[sz - 1]) +
           1;
  return 1;
}

static int stack_write_compact(struct reftable_stack *st,
             struct reftable_writer *wr,
             size_t first, size_t last,
             struct reftable_log_expiry_config *config)
{
  struct reftable_merged_table *mt = NULL;
  struct reftable_iterator it = { NULL };
  struct reftable_ref_record ref = { NULL };
  struct reftable_log_record log = { NULL };
  size_t subtabs_len = last - first + 1;
  uint64_t entries = 0;
  int err = 0;

  for (size_t i = first; i <= last; i++)
    st->stats.bytes += st->tables[i]->size;
  err = reftable_writer_set_limits(wr, st->tables[first]->min_update_index,
           st->tables[last]->max_update_index);
  if (err < 0)
    goto done;

  err = reftable_merged_table_new(&mt, st->tables + first, subtabs_len,
          st->opts.hash_id);
  if (err < 0)
    goto done;

  err = merged_table_init_iter(mt, &it, REFTABLE_BLOCK_TYPE_REF);
  if (err < 0)
    goto done;

  err = reftable_iterator_seek_ref(&it, "");
  if (err < 0)
    goto done;

  while (1) {
    err = reftable_iterator_next_ref(&it, &ref);
    if (err > 0) {
      err = 0;
      break;
    }
    if (err < 0)
      goto done;

    if (first == 0 && reftable_ref_record_is_deletion(&ref)) {
      continue;
    }

    err = reftable_writer_add_ref(wr, &ref);
    if (err < 0)
      goto done;
    entries++;
  }
  reftable_iterator_destroy(&it);

  err = merged_table_init_iter(mt, &it, REFTABLE_BLOCK_TYPE_LOG);
  if (err < 0)
    goto done;

  err = reftable_iterator_seek_log(&it, "");
  if (err < 0)
    goto done;

  while (1) {
    err = reftable_iterator_next_log(&it, &log);
    if (err > 0) {
      err = 0;
      break;
    }
    if (err < 0)
      goto done;
    if (first == 0 && reftable_log_record_is_deletion(&log)) {
      continue;
    }

    if (config && config->min_update_index > 0 &&
        log.update_index < config->min_update_index) {
      continue;
    }

    if (config && config->time > 0 &&
        log.value.update.time < config->time) {
      continue;
    }

    err = reftable_writer_add_log(wr, &log);
    if (err < 0)
      goto done;
    entries++;
  }

done:
  reftable_iterator_destroy(&it);
  if (mt)
    reftable_merged_table_free(mt);
  reftable_ref_record_release(&ref);
  reftable_log_record_release(&log);
  st->stats.entries_written += entries;
  return err;
}

static int stack_compact_locked(struct reftable_stack *st,
        size_t first, size_t last,
        struct reftable_log_expiry_config *config,
        const struct reftable_write_options *opts,
        struct reftable_tmpfile *tab_file_out)
{
  struct reftable_buf next_name = REFTABLE_BUF_INIT;
  struct reftable_buf tab_file_path = REFTABLE_BUF_INIT;
  struct reftable_writer *wr = NULL;
  struct fd_writer writer=  {
    .opts = opts,
  };
  struct reftable_tmpfile tab_file = REFTABLE_TMPFILE_INIT;
  int err = 0;

  err = format_name(&next_name, reftable_table_min_update_index(st->tables[first]),
        reftable_table_max_update_index(st->tables[last]));
  if (err < 0)
    goto done;

  err = stack_filename(&tab_file_path, st, next_name.buf);
  if (err < 0)
    goto done;

  err = reftable_buf_addstr(&tab_file_path, ".temp.XXXXXX");
  if (err < 0)
    goto done;

  err = tmpfile_from_pattern(&tab_file, tab_file_path.buf);
  if (err < 0)
    goto done;

  if (opts->default_permissions &&
      chmod(tab_file.path, opts->default_permissions) < 0) {
    err = REFTABLE_IO_ERROR;
    goto done;
  }

  writer.fd = tab_file.fd;
  err = reftable_writer_new(&wr, fd_writer_write, fd_writer_flush,
          &writer, st->opts.hash_id, opts);
  if (err < 0)
    goto done;

  err = stack_write_compact(st, wr, first, last, config);
  if (err < 0)
    goto done;

  err = reftable_writer_close(wr);
  if (err < 0)
    goto done;

  err = tmpfile_close(&tab_file);
  if (err < 0)
    goto done;

  *tab_file_out = tab_file;
  tab_file = REFTABLE_TMPFILE_INIT;

done:
  tmpfile_delete(&tab_file);
  reftable_writer_free(wr);
  reftable_buf_release(&next_name);
  reftable_buf_release(&tab_file_path);
  return err;
}

enum stack_compact_range_flags {
  /*
   * Perform a best-effort compaction. That is, even if we cannot lock
   * all tables in the specified range, we will try to compact the
   * remaining slice.
   */
  STACK_COMPACT_RANGE_BEST_EFFORT = (1 << 0),
};

/*
 * Compact all tables in the range `[first, last)` into a single new table.
 *
 * This function returns `0` on success or a code `< 0` on failure. When the
 * stack or any of the tables in the specified range are already locked then
 * this function returns `REFTABLE_LOCK_ERROR`. This is a benign error that
 * callers can either ignore, or they may choose to retry compaction after some
 * amount of time.
 */
static int stack_compact_range(struct reftable_stack *st,
             size_t first, size_t last,
             struct reftable_log_expiry_config *expiry,
             const struct reftable_write_options *opts,
             unsigned int flags)
{
  struct reftable_buf tables_list_buf = REFTABLE_BUF_INIT;
  struct reftable_buf new_table_name = REFTABLE_BUF_INIT;
  struct reftable_buf new_table_path = REFTABLE_BUF_INIT;
  struct reftable_buf table_name = REFTABLE_BUF_INIT;
  struct reftable_flock tables_list_lock = REFTABLE_FLOCK_INIT;
  struct reftable_flock *table_locks = NULL;
  struct reftable_tmpfile new_table = REFTABLE_TMPFILE_INIT;
  int is_empty_table = 0, err = 0;
  size_t first_to_replace, last_to_replace;
  size_t i, nlocks = 0;
  char **names = NULL;

  if (first > last || (!expiry && first == last)) {
    err = 0;
    goto done;
  }

  st->stats.attempts++;

  /*
   * Hold the lock so that we can read "tables.list" and lock all tables
   * which are part of the user-specified range.
   */
  err = flock_acquire(&tables_list_lock, st->list_file, opts->lock_timeout_ms);
  if (err < 0)
    goto done;

  /*
   * Check whether the stack is up-to-date. We unfortunately cannot
   * handle the situation gracefully in case it's _not_ up-to-date
   * because the range of tables that the user has requested us to
   * compact may have been changed. So instead we abort.
   *
   * We could in theory improve the situation by having the caller not
   * pass in a range, but instead the list of tables to compact. If so,
   * we could check that relevant tables still exist. But for now it's
   * good enough to just abort.
   */
  err = stack_uptodate(st, 0);
  if (err < 0)
    goto done;
  if (err > 0) {
    err = REFTABLE_OUTDATED_ERROR;
    goto done;
  }

  /*
   * Lock all tables in the user-provided range. This is the slice of our
   * stack which we'll compact.
   *
   * Note that we lock tables in reverse order from last to first. The
   * intent behind this is to allow a newer process to perform best
   * effort compaction of tables that it has added in the case where an
   * older process is still busy compacting tables which are preexisting
   * from the point of view of the newer process.
   */
  REFTABLE_ALLOC_ARRAY(table_locks, last - first + 1);
  if (!table_locks) {
    err = REFTABLE_OUT_OF_MEMORY_ERROR;
    goto done;
  }
  for (i = 0; i < last - first + 1; i++)
    table_locks[i] = REFTABLE_FLOCK_INIT;

  for (i = last + 1; i > first; i--) {
    err = stack_filename(&table_name, st, reftable_table_name(st->tables[i - 1]));
    if (err < 0)
      goto done;

    err = flock_acquire(&table_locks[nlocks], table_name.buf, 0);
    if (err < 0) {
      /*
       * When the table is locked already we may do a
       * best-effort compaction and compact only the tables
       * that we have managed to lock so far. This of course
       * requires that we have been able to lock at least two
       * tables, otherwise there would be nothing to compact.
       * In that case, we return a lock error to our caller.
       */
      if (err == REFTABLE_LOCK_ERROR && last - (i - 1) >= 2 &&
          flags & STACK_COMPACT_RANGE_BEST_EFFORT) {
        err = 0;
        /*
         * The subtraction is to offset the index, the
         * addition is to only compact up to the table
         * of the preceding iteration. They obviously
         * cancel each other out, but that may be
         * non-obvious when it was omitted.
         */
        first = (i - 1) + 1;
        break;
      }

      goto done;
    }

    /*
     * We need to close the lockfiles as we might otherwise easily
     * run into file descriptor exhaustion when we compress a lot
     * of tables.
     */
    err = flock_close(&table_locks[nlocks++]);
    if (err < 0)
      goto done;
  }

  /*
   * We have locked all tables in our range and can thus release the
   * "tables.list" lock while compacting the locked tables. This allows
   * concurrent updates to the stack to proceed.
   */
  err = flock_release(&tables_list_lock);
  if (err < 0) {
    err = REFTABLE_IO_ERROR;
    goto done;
  }

  /*
   * Compact the now-locked tables into a new table. Note that compacting
   * these tables may end up with an empty new table in case tombstones
   * end up cancelling out all refs in that range.
   */
  err = stack_compact_locked(st, first, last, expiry, opts, &new_table);
  if (err < 0) {
    if (err != REFTABLE_EMPTY_TABLE_ERROR)
      goto done;
    is_empty_table = 1;
  }

  /*
   * Now that we have written the new, compacted table we need to re-lock
   * "tables.list". We'll then replace the compacted range of tables with
   * the new table.
   */
  err = flock_acquire(&tables_list_lock, st->list_file, opts->lock_timeout_ms);
  if (err < 0)
    goto done;

  if (opts->default_permissions) {
    if (chmod(tables_list_lock.path,
        opts->default_permissions) < 0) {
      err = REFTABLE_IO_ERROR;
      goto done;
    }
  }

  /*
   * As we have unlocked the stack while compacting our slice of tables
   * it may have happened that a concurrently running process has updated
   * the stack while we were compacting. In that case, we need to check
   * whether the tables that we have just compacted still exist in the
   * stack in the exact same order as we have compacted them.
   *
   * If they do exist, then it is fine to continue and replace those
   * tables with our compacted version. If they don't, then we need to
   * abort.
   */
  err = stack_uptodate(st, 0);
  if (err < 0)
    goto done;
  if (err > 0) {
    ssize_t new_offset = -1;
    int fd;

    fd = open(st->list_file, O_RDONLY);
    if (fd < 0) {
      err = REFTABLE_IO_ERROR;
      goto done;
    }

    err = fd_read_lines(fd, &names);
    close(fd);
    if (err < 0)
      goto done;

    /*
     * Search for the offset of the first table that we have
     * compacted in the updated "tables.list" file.
     */
    for (size_t i = 0; names[i]; i++) {
      if (strcmp(names[i], st->tables[first]->name))
        continue;

      /*
       * We have found the first entry. Verify that all the
       * subsequent tables we have compacted still exist in
       * the modified stack in the exact same order as we
       * have compacted them.
       */
      for (size_t j = 1; j < last - first + 1; j++) {
        const char *old = first + j < st->merged->tables_len ?
          st->tables[first + j]->name : NULL;
        const char *new = names[i + j];

        /*
         * If some entries are missing or in case the tables
         * have changed then we need to bail out. Again, this
         * shouldn't ever happen because we have locked the
         * tables we are compacting.
         */
        if (!old || !new || strcmp(old, new)) {
          err = REFTABLE_OUTDATED_ERROR;
          goto done;
        }
      }

      new_offset = i;
      break;
    }

    /*
     * In case we didn't find our compacted tables in the stack we
     * need to bail out. In theory, this should have never happened
     * because we locked the tables we are compacting.
     */
    if (new_offset < 0) {
      err = REFTABLE_OUTDATED_ERROR;
      goto done;
    }

    /*
     * We have found the new range that we want to replace, so
     * let's update the range of tables that we want to replace.
     */
    first_to_replace = new_offset;
    last_to_replace = last + (new_offset - first);
  } else {
    /*
     * `fd_read_lines()` uses a `NULL` sentinel to indicate that
     * the array is at its end. As we use `free_names()` to free
     * the array, we need to include this sentinel value here and
     * thus have to allocate `tables_len + 1` many entries.
     */
    REFTABLE_CALLOC_ARRAY(names, st->merged->tables_len + 1);
    if (!names) {
      err = REFTABLE_OUT_OF_MEMORY_ERROR;
      goto done;
    }

    for (size_t i = 0; i < st->merged->tables_len; i++) {
      names[i] = reftable_strdup(st->tables[i]->name);
      if (!names[i]) {
        err = REFTABLE_OUT_OF_MEMORY_ERROR;
        goto done;
      }
    }
    first_to_replace = first;
    last_to_replace = last;
  }

  /*
   * If the resulting compacted table is not empty, then we need to move
   * it into place now.
   */
  if (!is_empty_table) {
    err = format_name(&new_table_name, st->tables[first]->min_update_index,
          st->tables[last]->max_update_index);
    if (err < 0)
      goto done;

    err = reftable_buf_addstr(&new_table_name, ".ref");
    if (err < 0)
      goto done;

    err = stack_filename(&new_table_path, st, new_table_name.buf);
    if (err < 0)
      goto done;

    err = tmpfile_rename(&new_table, new_table_path.buf);
    if (err < 0)
      goto done;
  }

  /*
   * Write the new "tables.list" contents with the compacted table we
   * have just written. In case the compacted table became empty we
   * simply skip writing it.
   */
  for (i = 0; i < first_to_replace; i++) {
    if ((err = reftable_buf_addstr(&tables_list_buf, names[i])) < 0 ||
        (err = reftable_buf_addstr(&tables_list_buf, "\n")) < 0)
          goto done;
  }
  if (!is_empty_table) {
    if ((err = reftable_buf_addstr(&tables_list_buf, new_table_name.buf)) < 0 ||
        (err = reftable_buf_addstr(&tables_list_buf, "\n")) < 0)
      goto done;
  }
  for (i = last_to_replace + 1; names[i]; i++) {
    if ((err = reftable_buf_addstr(&tables_list_buf, names[i])) < 0 ||
        (err = reftable_buf_addstr(&tables_list_buf, "\n")) < 0)
      goto done;
  }

  err = reftable_write_data(tables_list_lock.fd,
          tables_list_buf.buf, tables_list_buf.len);
  if (err < 0) {
    err = REFTABLE_IO_ERROR;
    unlink(new_table_path.buf);
    goto done;
  }

  err = fsync(tables_list_lock.fd);
  if (err < 0) {
    err = REFTABLE_IO_ERROR;
    unlink(new_table_path.buf);
    goto done;
  }

  err = flock_commit(&tables_list_lock);
  if (err < 0) {
    err = REFTABLE_IO_ERROR;
    unlink(new_table_path.buf);
    goto done;
  }

  /*
   * Reload the stack before deleting the compacted tables. We can only
   * delete the files after we closed them on Windows, so this needs to
   * happen first.
   */
  err = reftable_stack_reload_maybe_reuse(st, first < last);
  if (err < 0)
    goto done;

  /*
   * Delete the old tables. They may still be in use by concurrent
   * readers, so it is expected that unlinking tables may fail.
   */
  for (i = 0; i < nlocks; i++) {
    struct reftable_flock *table_lock = &table_locks[i];

    reftable_buf_reset(&table_name);
    err = reftable_buf_add(&table_name, table_lock->path,
               strlen(table_lock->path) - strlen(".lock"));
    if (err)
      continue;

    unlink(table_name.buf);
  }

done:
  flock_release(&tables_list_lock);
  for (i = 0; table_locks && i < nlocks; i++)
    flock_release(&table_locks[i]);
  reftable_free(table_locks);

  tmpfile_delete(&new_table);
  reftable_buf_release(&new_table_name);
  reftable_buf_release(&new_table_path);
  reftable_buf_release(&tables_list_buf);
  reftable_buf_release(&table_name);
  free_names(names);

  if (err == REFTABLE_LOCK_ERROR)
    st->stats.failures++;

  return err;
}

int reftable_stack_compact_all(struct reftable_stack *st,
             const struct reftable_write_options *opts,
             struct reftable_log_expiry_config *config)
{
  struct reftable_write_options opts_default = { 0 };
  size_t last = st->merged->tables_len ? st->merged->tables_len - 1 : 0;

  if (!opts)
    opts = &opts_default;

  return stack_compact_range(st, 0, last, config, opts, 0);
}

static int segment_size(struct segment *s)
{
  return s->end - s->start;
}

struct segment suggest_compaction_segment(uint64_t *sizes, size_t n,
            uint8_t factor)
{
  struct segment seg = { 0 };
  uint64_t bytes;
  size_t i;

  if (!factor)
    factor = DEFAULT_GEOMETRIC_FACTOR;

  /*
   * If there are no tables or only a single one then we don't have to
   * compact anything. The sequence is geometric by definition already.
   */
  if (n <= 1)
    return seg;

  /*
   * Find the ending table of the compaction segment needed to restore the
   * geometric sequence. Note that the segment end is exclusive.
   *
   * To do so, we iterate backwards starting from the most recent table
   * until a valid segment end is found. If the preceding table is smaller
   * than the current table multiplied by the geometric factor (2), the
   * compaction segment end has been identified.
   *
   * Tables after the ending point are not added to the byte count because
   * they are already valid members of the geometric sequence. Due to the
   * properties of a geometric sequence, it is not possible for the sum of
   * these tables to exceed the value of the ending point table.
   *
   * Example table size sequence requiring no compaction:
   *  64, 32, 16, 8, 4, 2, 1
   *
   * Example table size sequence where compaction segment end is set to
   * the last table. Since the segment end is exclusive, the last table is
   * excluded during subsequent compaction and the table with size 3 is
   * the final table included:
   *  64, 32, 16, 8, 4, 3, 1
   */
  for (i = n - 1; i > 0; i--) {
    if (sizes[i - 1] < sizes[i] * factor) {
      seg.end = i + 1;
      bytes = sizes[i];
      break;
    }
  }

  /*
   * Find the starting table of the compaction segment by iterating
   * through the remaining tables and keeping track of the accumulated
   * size of all tables seen from the segment end table. The previous
   * table is compared to the accumulated size because the tables from the
   * segment end are merged backwards recursively.
   *
   * Note that we keep iterating even after we have found the first
   * starting point. This is because there may be tables in the stack
   * preceding that first starting point which violate the geometric
   * sequence.
   *
   * Example compaction segment start set to table with size 32:
   *  128, 32, 16, 8, 4, 3, 1
   */
  for (; i > 0; i--) {
    uint64_t curr = bytes;
    bytes += sizes[i - 1];

    if (sizes[i - 1] < curr * factor) {
      seg.start = i - 1;
      seg.bytes = bytes;
    }
  }

  return seg;
}

static int stack_segments_for_compaction(struct reftable_stack *st,
           const struct reftable_write_options *opts,
           struct segment *seg)
{
  int version = (st->opts.hash_id == REFTABLE_HASH_SHA1) ? 1 : 2;
  int overhead = header_size(version) - 1;
  uint64_t *sizes;

  REFTABLE_CALLOC_ARRAY(sizes, st->merged->tables_len);
  if (!sizes)
    return REFTABLE_OUT_OF_MEMORY_ERROR;

  for (size_t i = 0; i < st->merged->tables_len; i++)
    sizes[i] = st->tables[i]->size - overhead;

  *seg = suggest_compaction_segment(sizes, st->merged->tables_len,
            opts->auto_compaction_factor);
  reftable_free(sizes);

  return 0;
}

static int update_segment_if_compaction_required(struct reftable_stack *st,
             const struct reftable_write_options *opts,
             struct segment *seg,
             bool use_geometric,
             bool *required)
{
  int err;

  if (st->merged->tables_len < 2) {
    *required = false;
    return 0;
  }

  if (!use_geometric) {
    *required = true;
    return 0;
  }

  err = stack_segments_for_compaction(st, opts, seg);
  if (err)
    return err;

  *required = segment_size(seg) > 0;
  return 0;
}

int reftable_stack_compaction_required(struct reftable_stack *st,
               const struct reftable_write_options *opts,
               bool use_heuristics,
               bool *required)
{
  struct reftable_write_options opts_default = { 0 };
  struct segment seg;

  if (!opts)
    opts = &opts_default;

  return update_segment_if_compaction_required(st, opts, &seg,
                 use_heuristics, required);
}

int reftable_stack_auto_compact(struct reftable_stack *st,
        const struct reftable_write_options *opts)
{
  struct reftable_write_options opts_default = { 0 };
  struct segment seg;
  bool required;
  int err;

  if (!opts)
    opts = &opts_default;

  err = update_segment_if_compaction_required(st, opts, &seg, true,
                &required);
  if (err)
    return err;

  if (required)
    return stack_compact_range(st, seg.start, seg.end - 1,
             NULL, opts,
             STACK_COMPACT_RANGE_BEST_EFFORT);

  return 0;
}

struct reftable_compaction_stats *
reftable_stack_compaction_stats(struct reftable_stack *st)
{
  return &st->stats;
}

int reftable_stack_read_ref(struct reftable_stack *st, const char *refname,
          struct reftable_ref_record *ref)
{
  struct reftable_iterator it = { 0 };
  int ret;

  ret = reftable_merged_table_init_ref_iterator(st->merged, &it);
  if (ret)
    goto out;

  ret = reftable_iterator_seek_ref(&it, refname);
  if (ret)
    goto out;

  ret = reftable_iterator_next_ref(&it, ref);
  if (ret)
    goto out;

  if (strcmp(ref->refname, refname) ||
      reftable_ref_record_is_deletion(ref)) {
    reftable_ref_record_release(ref);
    ret = 1;
    goto out;
  }

out:
  reftable_iterator_destroy(&it);
  return ret;
}

int reftable_stack_read_log(struct reftable_stack *st, const char *refname,
          struct reftable_log_record *log)
{
  struct reftable_iterator it = {0};
  int err;

  err = reftable_stack_init_log_iterator(st, &it);
  if (err)
    goto done;

  err = reftable_iterator_seek_log(&it, refname);
  if (err)
    goto done;

  err = reftable_iterator_next_log(&it, log);
  if (err)
    goto done;

  if (strcmp(log->refname, refname) ||
      reftable_log_record_is_deletion(log)) {
    err = 1;
    goto done;
  }

done:
  if (err) {
    reftable_log_record_release(log);
  }
  reftable_iterator_destroy(&it);
  return err;
}

static int is_table_name(const char *s)
{
  const char *dot = strrchr(s, '.');
  return dot && !strcmp(dot, ".ref");
}

static void remove_maybe_stale_table(struct reftable_stack *st, uint64_t max,
             const char *name)
{
  int err = 0;
  uint64_t update_idx = 0;
  struct reftable_block_source src = { NULL };
  struct reftable_table *table = NULL;
  struct reftable_buf table_path = REFTABLE_BUF_INIT;

  err = stack_filename(&table_path, st, name);
  if (err < 0)
    goto done;

  err = reftable_block_source_from_file(&src, table_path.buf);
  if (err < 0)
    goto done;

  err = reftable_table_new(&table, &src, name);
  if (err < 0)
    goto done;

  update_idx = reftable_table_max_update_index(table);
  reftable_table_decref(table);

  if (update_idx <= max) {
    unlink(table_path.buf);
  }
done:
  reftable_buf_release(&table_path);
}

static int reftable_stack_clean_locked(struct reftable_stack *st)
{
  uint64_t max = reftable_merged_table_max_update_index(
    reftable_stack_merged_table(st));
  DIR *dir = opendir(st->reftable_dir);
  struct dirent *d = NULL;
  if (!dir) {
    return REFTABLE_IO_ERROR;
  }

  while ((d = readdir(dir))) {
    int found = 0;
    if (!is_table_name(d->d_name))
      continue;

    for (size_t i = 0; !found && i < st->tables_len; i++)
      found = !strcmp(reftable_table_name(st->tables[i]), d->d_name);
    if (found)
      continue;

    remove_maybe_stale_table(st, max, d->d_name);
  }

  closedir(dir);
  return 0;
}

int reftable_stack_clean(struct reftable_stack *st)
{
  struct reftable_addition *add = NULL;
  int err = reftable_stack_addition_new(&add, st, NULL);
  if (err < 0) {
    goto done;
  }

  err = reftable_stack_clean_locked(st);

done:
  reftable_addition_destroy(add);
  return err;
}

enum reftable_hash reftable_stack_hash_id(struct reftable_stack *st)
{
  return reftable_merged_table_hash_id(st->merged);
}

Coverage Report

Created: 2026-10-17 07:15