nix/sys/
memfd.rs

1//! Interfaces for managing memory-backed files.
2
3use cfg_if::cfg_if;
4use std::os::unix::io::{FromRawFd, OwnedFd, RawFd};
5
6use crate::errno::Errno;
7use crate::Result;
8use std::ffi::CStr;
9
10libc_bitflags!(
11    /// Options that change the behavior of [`memfd_create`].
12    pub struct MemFdCreateFlag: libc::c_uint {
13        /// Set the close-on-exec ([`FD_CLOEXEC`]) flag on the new file descriptor.
14        ///
15        /// By default, the new file descriptor is set to remain open across an [`execve`]
16        /// (the `FD_CLOEXEC` flag is initially disabled). This flag can be used to change
17        /// this default. The file offset is set to the beginning of the file (see [`lseek`]).
18        ///
19        /// See also the description of the `O_CLOEXEC` flag in [`open(2)`].
20        ///
21        /// [`execve`]: crate::unistd::execve
22        /// [`lseek`]: crate::unistd::lseek
23        /// [`FD_CLOEXEC`]: crate::fcntl::FdFlag::FD_CLOEXEC
24        /// [`open(2)`]: https://man7.org/linux/man-pages/man2/open.2.html
25        MFD_CLOEXEC;
26        /// Allow sealing operations on this file.
27        ///
28        /// See also the file sealing notes given in [`memfd_create(2)`].
29        ///
30        /// [`memfd_create(2)`]: https://man7.org/linux/man-pages/man2/memfd_create.2.html
31        MFD_ALLOW_SEALING;
32        /// Anonymous file will be created using huge pages. It should be safe now to
33        /// combine with [`MFD_ALLOW_SEALING`] too.
34        /// However, despite its presence, on FreeBSD it is unimplemented for now (ENOSYS).
35        ///
36        /// See also the hugetlb filesystem in [`memfd_create(2)`].
37        ///
38        /// [`memfd_create(2)`]: https://man7.org/linux/man-pages/man2/memfd_create.2.html
39        #[cfg(linux_android)]
40        MFD_HUGETLB;
41        /// Following are to be used with [`MFD_HUGETLB`], indicating the desired hugetlb size.
42        ///
43        /// See also the hugetlb filesystem in [`memfd_create(2)`].
44        ///
45        /// [`memfd_create(2)`]: https://man7.org/linux/man-pages/man2/memfd_create.2.html
46        #[cfg(linux_android)]
47        MFD_HUGE_1MB;
48        /// hugetlb size of 2MB.
49        #[cfg(linux_android)]
50        MFD_HUGE_2MB;
51        /// hugetlb size of 8MB.
52        #[cfg(linux_android)]
53        MFD_HUGE_8MB;
54        /// hugetlb size of 16MB.
55        #[cfg(linux_android)]
56        MFD_HUGE_16MB;
57        /// hugetlb size of 32MB.
58        #[cfg(linux_android)]
59        MFD_HUGE_32MB;
60        /// hugetlb size of 256MB.
61        #[cfg(linux_android)]
62        MFD_HUGE_256MB;
63        /// hugetlb size of 512MB.
64        #[cfg(linux_android)]
65        MFD_HUGE_512MB;
66        /// hugetlb size of 1GB.
67        #[cfg(linux_android)]
68        MFD_HUGE_1GB;
69        /// hugetlb size of 2GB.
70        #[cfg(linux_android)]
71        MFD_HUGE_2GB;
72        /// hugetlb size of 16GB.
73        #[cfg(linux_android)]
74        MFD_HUGE_16GB;
75    }
76);
77
78/// Creates an anonymous file that lives in memory, and return a file-descriptor to it.
79///
80/// The file behaves like a regular file, and so can be modified, truncated, memory-mapped, and so on.
81/// However, unlike a regular file, it lives in RAM and has a volatile backing storage.
82///
83/// For more information, see [`memfd_create(2)`].
84///
85/// [`memfd_create(2)`]: https://man7.org/linux/man-pages/man2/memfd_create.2.html
86#[inline] // Delays codegen, preventing linker errors with dylibs and --no-allow-shlib-undefined
87pub fn memfd_create(name: &CStr, flags: MemFdCreateFlag) -> Result<OwnedFd> {
88    let res = unsafe {
89        cfg_if! {
90            if #[cfg(all(
91                // Android does not have a memfd_create symbol
92                not(target_os = "android"),
93                any(
94                    target_os = "freebsd",
95                    // If the OS is Linux, gnu and musl expose a memfd_create symbol but not uclibc
96                    target_env = "gnu",
97                    target_env = "musl",
98                )))]
99            {
100                libc::memfd_create(name.as_ptr(), flags.bits())
101            } else {
102                libc::syscall(libc::SYS_memfd_create, name.as_ptr(), flags.bits())
103            }
104        }
105    };
106
107    Errno::result(res).map(|r| unsafe { OwnedFd::from_raw_fd(r as RawFd) })
108}
nix/sys/memfd.rs

nix/sys/
memfd.rs
