nix/sys/
memfd.rs

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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::{NixPath, Result};
8
9libc_bitflags!(
10    /// Options that change the behavior of [`memfd_create`].
11    pub struct MFdFlags: libc::c_uint {
12        /// Set the close-on-exec ([`FD_CLOEXEC`]) flag on the new file descriptor.
13        ///
14        /// By default, the new file descriptor is set to remain open across an [`execve`]
15        /// (the `FD_CLOEXEC` flag is initially disabled). This flag can be used to change
16        /// this default. The file offset is set to the beginning of the file (see [`lseek`]).
17        ///
18        /// See also the description of the `O_CLOEXEC` flag in [`open(2)`].
19        ///
20        /// [`execve`]: crate::unistd::execve
21        /// [`lseek`]: crate::unistd::lseek
22        /// [`FD_CLOEXEC`]: crate::fcntl::FdFlag::FD_CLOEXEC
23        /// [`open(2)`]: https://man7.org/linux/man-pages/man2/open.2.html
24        MFD_CLOEXEC;
25        /// Allow sealing operations on this file.
26        ///
27        /// See also the file sealing notes given in [`memfd_create(2)`].
28        ///
29        /// [`memfd_create(2)`]: https://man7.org/linux/man-pages/man2/memfd_create.2.html
30        MFD_ALLOW_SEALING;
31        /// Anonymous file will be created using huge pages. It should be safe now to
32        /// combine with [`MFD_ALLOW_SEALING`] too.
33        /// However, despite its presence, on FreeBSD it is unimplemented for now (ENOSYS).
34        ///
35        /// See also the hugetlb filesystem in [`memfd_create(2)`].
36        ///
37        /// [`memfd_create(2)`]: https://man7.org/linux/man-pages/man2/memfd_create.2.html
38        #[cfg(linux_android)]
39        MFD_HUGETLB;
40        /// Shift to get the huge page size.
41        #[cfg(target_env = "ohos")]
42        MFD_HUGE_SHIFT;
43        /// Mask to get the huge page size.
44        #[cfg(target_env = "ohos")]
45        MFD_HUGE_MASK;
46        /// hugetlb size of 64KB.
47        #[cfg(target_env = "ohos")]
48        MFD_HUGE_64KB;
49        /// hugetlb size of 512KB.
50        #[cfg(target_env = "ohos")]
51        MFD_HUGE_512KB;
52        /// Following are to be used with [`MFD_HUGETLB`], indicating the desired hugetlb size.
53        ///
54        /// See also the hugetlb filesystem in [`memfd_create(2)`].
55        ///
56        /// [`memfd_create(2)`]: https://man7.org/linux/man-pages/man2/memfd_create.2.html
57        #[cfg(linux_android)]
58        MFD_HUGE_1MB;
59        /// hugetlb size of 2MB.
60        #[cfg(linux_android)]
61        MFD_HUGE_2MB;
62        /// hugetlb size of 8MB.
63        #[cfg(linux_android)]
64        MFD_HUGE_8MB;
65        /// hugetlb size of 16MB.
66        #[cfg(linux_android)]
67        MFD_HUGE_16MB;
68        /// hugetlb size of 32MB.
69        #[cfg(linux_android)]
70        MFD_HUGE_32MB;
71        /// hugetlb size of 256MB.
72        #[cfg(linux_android)]
73        MFD_HUGE_256MB;
74        /// hugetlb size of 512MB.
75        #[cfg(linux_android)]
76        MFD_HUGE_512MB;
77        /// hugetlb size of 1GB.
78        #[cfg(linux_android)]
79        MFD_HUGE_1GB;
80        /// hugetlb size of 2GB.
81        #[cfg(linux_android)]
82        MFD_HUGE_2GB;
83        /// hugetlb size of 16GB.
84        #[cfg(linux_android)]
85        MFD_HUGE_16GB;
86    }
87);
88
89#[deprecated(since = "0.30.0", note = "Use `MFdFlags instead`")]
90/// The deprecated MemFdCreateFlag type alias
91pub type MemFdCreateFlag = MFdFlags;
92
93/// Creates an anonymous file that lives in memory, and return a file-descriptor to it.
94///
95/// The file behaves like a regular file, and so can be modified, truncated, memory-mapped, and so on.
96/// However, unlike a regular file, it lives in RAM and has a volatile backing storage.
97///
98/// For more information, see [`memfd_create(2)`].
99///
100/// [`memfd_create(2)`]: https://man7.org/linux/man-pages/man2/memfd_create.2.html
101#[inline] // Delays codegen, preventing linker errors with dylibs and --no-allow-shlib-undefined
102pub fn memfd_create<P: NixPath + ?Sized>(
103    name: &P,
104    flags: MFdFlags,
105) -> Result<OwnedFd> {
106    let res = name.with_nix_path(|cstr| {
107        unsafe {
108            cfg_if! {
109            if #[cfg(all(
110                // Android does not have a memfd_create symbol
111                not(target_os = "android"),
112                any(
113                    target_os = "freebsd",
114                    // If the OS is Linux, gnu/musl/ohos expose a memfd_create symbol but not uclibc
115                    target_env = "gnu",
116                    target_env = "musl",
117                    target_env = "ohos"
118                )))]
119            {
120                libc::memfd_create(cstr.as_ptr(), flags.bits())
121            } else {
122                libc::syscall(libc::SYS_memfd_create, cstr.as_ptr(), flags.bits())
123            }
124        }
125        }
126    })?;
127
128    Errno::result(res).map(|r| unsafe { OwnedFd::from_raw_fd(r as RawFd) })
129}
nix/sys/memfd.rs

nix/sys/
memfd.rs
