/* Copyright (c) 2008, 2009, 2010, 2011, 2012, 2013, 2014 Nicira, Inc.

 *

 * Licensed under the Apache License, Version 2.0 (the "License");

 * you may not use this file except in compliance with the License.

 * You may obtain a copy of the License at:

 *

 *     http://www.apache.org/licenses/LICENSE-2.0

 *

 * Unless required by applicable law or agreed to in writing, software

 * distributed under the License is distributed on an "AS IS" BASIS,

 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

 * See the License for the specific language governing permissions and

 * limitations under the License.

 */

#include <config.h>

#include "lockfile.h"

#include <errno.h>

#include <fcntl.h>

#include <stdlib.h>

#include <string.h>

#include <sys/stat.h>

#include <unistd.h>

#include "coverage.h"

#include "hash.h"

#include "openvswitch/hmap.h"

#include "ovs-thread.h"

#include "timeval.h"

#include "util.h"

#include "openvswitch/vlog.h"

VLOG_DEFINE_THIS_MODULE(lockfile);

COVERAGE_DEFINE(lockfile_lock);

COVERAGE_DEFINE(lockfile_error);

COVERAGE_DEFINE(lockfile_unlock);

struct lockfile {

    struct hmap_node hmap_node;

    char *name;

    dev_t device;

    ino_t inode;

    int fd;

};

/* Lock table.

 *

 * We have to do this stupid dance because POSIX says that closing *any* file

 * descriptor for a file on which a process holds a lock drops *all* locks on

 * that file.  That means that we can't afford to open a lockfile more than

 * once. */

static struct ovs_mutex lock_table_mutex = OVS_MUTEX_INITIALIZER;

static struct hmap lock_table__ = HMAP_INITIALIZER(&lock_table__);

static struct hmap *const lock_table OVS_GUARDED_BY(lock_table_mutex)

    = &lock_table__;

static void lockfile_unhash(struct lockfile *);

static int lockfile_try_lock(const char *name, pid_t *pidp,

                             struct lockfile **lockfilep)

    OVS_REQUIRES(lock_table_mutex);

static void lockfile_do_unlock(struct lockfile * lockfile)

    OVS_REQUIRES(lock_table_mutex);

/* Returns the name of the lockfile that would be created for locking a file

 * named 'filename_'.  The caller is responsible for freeing the returned name,

 * with free(), when it is no longer needed. */

char *

lockfile_name(const char *filename_)

{

    char *filename;

    const char *slash;

    char *lockname;

    /* If 'filename_' is a symlink, base the name of the lockfile on the

     * symlink's target rather than the name of the symlink.  That way, if a

     * file is symlinked, but there is no symlink for its lockfile, then there

     * is only a single lockfile for both the source and the target of the

     * symlink, not one for each. */

    filename = follow_symlinks(filename_);

    slash = strrchr(filename, '/');

    lockname = (slash

                ? xasprintf("%.*s/.%s.~lock~",

                            (int) (slash - filename), filename, slash + 1)

                : xasprintf(".%s.~lock~", filename));

    free(filename);

    return lockname;

}

/* Locks the configuration file against modification by other processes and

 * re-reads it from disk.

 *

 * Returns 0 on success, otherwise a positive errno value.  On success,

 * '*lockfilep' is set to point to a new "struct lockfile *" that may be

 * unlocked with lockfile_unlock().  On failure, '*lockfilep' is set to

 * NULL.  Will not block if the lock cannot be immediately acquired. */

int

lockfile_lock(const char *file, struct lockfile **lockfilep)

{

    /* Only exclusive ("write") locks are supported.  This is not a problem

     * because the Open vSwitch code that currently uses lock files does so in

     * stylized ways such that any number of readers may access a file while it

     * is being written. */

    char *lock_name;

    pid_t pid;

    int error;

    COVERAGE_INC(lockfile_lock);

    lock_name = lockfile_name(file);

    ovs_mutex_lock(&lock_table_mutex);

    error = lockfile_try_lock(lock_name, &pid, lockfilep);

    ovs_mutex_unlock(&lock_table_mutex);

    if (error) {

        COVERAGE_INC(lockfile_error);

        if (error == EACCES) {

            error = EAGAIN;

        }

        if (pid == getpid()) {

            VLOG_WARN("%s: cannot lock file because this process has already "

                      "locked it", lock_name);

        } else if (pid) {

            VLOG_WARN("%s: cannot lock file because it is already locked by "

                      "pid %ld", lock_name, (long int) pid);

        } else {

            VLOG_WARN("%s: failed to lock file: %s",

                      lock_name, ovs_strerror(error));

        }

    }

    free(lock_name);

    return error;

}

/* Unlocks 'lockfile', which must have been created by a call to

 * lockfile_lock(), and frees 'lockfile'. */

void

lockfile_unlock(struct lockfile *lockfile)

{

    if (lockfile) {

        ovs_mutex_lock(&lock_table_mutex);

        lockfile_do_unlock(lockfile);

        ovs_mutex_unlock(&lock_table_mutex);

        COVERAGE_INC(lockfile_unlock);

        free(lockfile->name);

        free(lockfile);

    }

}

/* Marks all the currently locked lockfiles as no longer locked.  It makes

 * sense to call this function after fork(), because a child created by fork()

 * does not hold its parents' locks. */

void

lockfile_postfork(void)

{

    struct lockfile *lockfile;

    ovs_mutex_lock(&lock_table_mutex);

    HMAP_FOR_EACH (lockfile, hmap_node, lock_table) {

        if (lockfile->fd >= 0) {

            VLOG_WARN("%s: child does not inherit lock", lockfile->name);

            lockfile_unhash(lockfile);

        }

    }

    ovs_mutex_unlock(&lock_table_mutex);

}

static uint32_t

lockfile_hash(dev_t device, ino_t inode)

{

    return hash_bytes(&device, sizeof device,

                      hash_bytes(&inode, sizeof inode, 0));

}

static struct lockfile *

lockfile_find(dev_t device, ino_t inode) OVS_REQUIRES(lock_table_mutex)

{

    struct lockfile *lockfile;

    HMAP_FOR_EACH_WITH_HASH (lockfile, hmap_node,

                             lockfile_hash(device, inode), lock_table) {

        if (lockfile->device == device && lockfile->inode == inode) {

            return lockfile;

        }

    }

    return NULL;

}

static void

lockfile_unhash(struct lockfile *lockfile) OVS_REQUIRES(lock_table_mutex)

{

    if (lockfile->fd >= 0) {

        close(lockfile->fd);

        lockfile->fd = -1;

        hmap_remove(lock_table, &lockfile->hmap_node);

    }

}

static struct lockfile *

lockfile_register(const char *name, dev_t device, ino_t inode, int fd)

    OVS_REQUIRES(lock_table_mutex)

{

    struct lockfile *lockfile;

    lockfile = lockfile_find(device, inode);

    if (lockfile) {

        VLOG_ERR("%s: lock file disappeared and reappeared!", name);

        lockfile_unhash(lockfile);

    }

    lockfile = xmalloc(sizeof *lockfile);

    lockfile->name = xstrdup(name);

    lockfile->device = device;

    lockfile->inode = inode;

    lockfile->fd = fd;

    hmap_insert(lock_table, &lockfile->hmap_node,

                lockfile_hash(device, inode));

    return lockfile;

}

static void

lockfile_do_unlock(struct lockfile *lockfile)

{

    lockfile_unhash(lockfile);

}

static int

lockfile_try_lock(const char *name, pid_t *pidp, struct lockfile **lockfilep)

    OVS_REQUIRES(lock_table_mutex)

{

    struct flock l;

    struct stat s;

    int error;

    int fd;

    *lockfilep = NULL;

    *pidp = 0;

    /* Check whether we've already got a lock on that file. */

    if (!stat(name, &s)) {

        if (lockfile_find(s.st_dev, s.st_ino)) {

            *pidp = getpid();

            return EDEADLK;

        }

    } else if (errno != ENOENT) {

        VLOG_WARN("%s: failed to stat lock file: %s",

                  name, ovs_strerror(errno));

        return errno;

    }

    /* Open the lock file. */

    fd = open(name, O_RDWR | O_CREAT, 0600);

    if (fd < 0) {

        VLOG_WARN("%s: failed to open lock file: %s",

                  name, ovs_strerror(errno));

        return errno;

    }

    /* Get the inode and device number for the lock table. */

    if (fstat(fd, &s)) {

        VLOG_ERR("%s: failed to fstat lock file: %s",

                 name, ovs_strerror(errno));

        close(fd);

        return errno;

    }

    /* Try to lock the file. */

    memset(&l, 0, sizeof l);

    l.l_type = F_WRLCK;

    l.l_whence = SEEK_SET;

    l.l_start = 0;

    l.l_len = 0;

    error = fcntl(fd, F_SETLK, &l) == -1 ? errno : 0;

    if (!error) {

        *lockfilep = lockfile_register(name, s.st_dev, s.st_ino, fd);

    } else {

        if (!fcntl(fd, F_GETLK, &l) && l.l_type != F_UNLCK) {

            *pidp = l.l_pid;

        }

        close(fd);

    }

    return error;

}