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: i32 = 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: i32| unsafe { OwnedFd::from_raw_fd(r as RawFd) })
108}
109