Coverage Report

Created: 2026-01-27 06:25

next uncovered line (L), next uncovered region (R), next uncovered branch (B)
/rust/registry/src/index.crates.io-1949cf8c6b5b557f/nix-0.28.0/src/sys/memfd.rs
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//! Interfaces for managing memory-backed files.
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use cfg_if::cfg_if;
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use std::os::unix::io::{FromRawFd, OwnedFd, RawFd};
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use crate::errno::Errno;
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use crate::Result;
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use std::ffi::CStr;
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libc_bitflags!(
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    /// Options that change the behavior of [`memfd_create`].
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    pub struct MemFdCreateFlag: libc::c_uint {
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        /// Set the close-on-exec ([`FD_CLOEXEC`]) flag on the new file descriptor.
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        ///
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        /// By default, the new file descriptor is set to remain open across an [`execve`]
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        /// (the `FD_CLOEXEC` flag is initially disabled). This flag can be used to change
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        /// this default. The file offset is set to the beginning of the file (see [`lseek`]).
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        ///
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        /// See also the description of the `O_CLOEXEC` flag in [`open(2)`].
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        ///
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        /// [`execve`]: crate::unistd::execve
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        /// [`lseek`]: crate::unistd::lseek
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        /// [`FD_CLOEXEC`]: crate::fcntl::FdFlag::FD_CLOEXEC
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        /// [`open(2)`]: https://man7.org/linux/man-pages/man2/open.2.html
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        MFD_CLOEXEC;
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        /// Allow sealing operations on this file.
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        ///
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        /// See also the file sealing notes given in [`memfd_create(2)`].
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        ///
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        /// [`memfd_create(2)`]: https://man7.org/linux/man-pages/man2/memfd_create.2.html
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        MFD_ALLOW_SEALING;
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        /// Anonymous file will be created using huge pages. It should be safe now to
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        /// combine with [`MFD_ALLOW_SEALING`] too.
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        /// However, despite its presence, on FreeBSD it is unimplemented for now (ENOSYS).
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        ///
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        /// See also the hugetlb filesystem in [`memfd_create(2)`].
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        ///
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        /// [`memfd_create(2)`]: https://man7.org/linux/man-pages/man2/memfd_create.2.html
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        #[cfg(linux_android)]
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        MFD_HUGETLB;
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        /// Following are to be used with [`MFD_HUGETLB`], indicating the desired hugetlb size.
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        ///
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        /// See also the hugetlb filesystem in [`memfd_create(2)`].
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        ///
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        /// [`memfd_create(2)`]: https://man7.org/linux/man-pages/man2/memfd_create.2.html
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        #[cfg(linux_android)]
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        MFD_HUGE_1MB;
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        /// hugetlb size of 2MB.
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        #[cfg(linux_android)]
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        MFD_HUGE_2MB;
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        /// hugetlb size of 8MB.
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        #[cfg(linux_android)]
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        MFD_HUGE_8MB;
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        /// hugetlb size of 16MB.
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        #[cfg(linux_android)]
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        MFD_HUGE_16MB;
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        /// hugetlb size of 32MB.
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        #[cfg(linux_android)]
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        MFD_HUGE_32MB;
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        /// hugetlb size of 256MB.
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        #[cfg(linux_android)]
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        MFD_HUGE_256MB;
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        /// hugetlb size of 512MB.
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        #[cfg(linux_android)]
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        MFD_HUGE_512MB;
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        /// hugetlb size of 1GB.
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        #[cfg(linux_android)]
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        MFD_HUGE_1GB;
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        /// hugetlb size of 2GB.
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        #[cfg(linux_android)]
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        MFD_HUGE_2GB;
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        /// hugetlb size of 16GB.
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        #[cfg(linux_android)]
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        MFD_HUGE_16GB;
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    }
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);
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/// Creates an anonymous file that lives in memory, and return a file-descriptor to it.
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///
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/// The file behaves like a regular file, and so can be modified, truncated, memory-mapped, and so on.
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/// However, unlike a regular file, it lives in RAM and has a volatile backing storage.
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///
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/// For more information, see [`memfd_create(2)`].
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///
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/// [`memfd_create(2)`]: https://man7.org/linux/man-pages/man2/memfd_create.2.html
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#[inline] // Delays codegen, preventing linker errors with dylibs and --no-allow-shlib-undefined
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pub fn memfd_create(name: &CStr, flags: MemFdCreateFlag) -> Result<OwnedFd> {
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    let res = unsafe {
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        cfg_if! {
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            if #[cfg(all(
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                // Android does not have a memfd_create symbol
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                not(target_os = "android"),
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                any(
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                    target_os = "freebsd",
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                    // If the OS is Linux, gnu and musl expose a memfd_create symbol but not uclibc
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                    target_env = "gnu",
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                    target_env = "musl",
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                )))]
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            {
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                libc::memfd_create(name.as_ptr(), flags.bits())
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            } else {
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                libc::syscall(libc::SYS_memfd_create, name.as_ptr(), flags.bits())
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            }
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        }
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    };
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    Errno::result(res).map(|r| unsafe { OwnedFd::from_raw_fd(r as RawFd) })
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0
}