mount/linux: add a safe wrapper for open_tree(2) #1958
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lucab
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Mmh, it looks like the |
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Ok, I landed several fixes in |
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@rtzoeller @asomers may I ask for a review on this one? |
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Sorry for such a slow response! And thanks for you work! I have left some comments on this PR :) |
This adds an ergonomic wrapper for the Linux-specific `open_tree(2)` syscall, using safe-io file descriptors. The syscall has been introduced in kernel version 5.2 and allows FD-based manipulation of mount hierarchies.
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@SteveLauC thanks for the review! (And no need to apologise 💙) |
| - Added `mount::open_tree()` helper on Linux. | ||
| ([#1958](https://github.com/nix-rust/nix/pull/1958)) | ||
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We have changed our changelog mode in #2149 (the old one is way too conflict-prone), please see CONTRIBUTING.md on how to add a changelog
| flags: OpenTreeFlags, | ||
| ) -> Result<OwnedFd> { | ||
| let res = pathname.with_nix_path(|cstr| unsafe { | ||
| let raw_dirfd = at_rawfd(dirfd.map(|v| v.as_fd().as_raw_fd())); |
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at_rawfd() has been gated with:
#[cfg(any(
all(feature = "fs", not(target_os = "redox")),
all(feature = "process", any(target_os = "android", target_os = "linux"))
))]
pub(crate) fn at_rawfd(fd: Option<RawFd>) -> raw::c_int {
fd.unwrap_or(libc::AT_FDCWD)
}Given that open_tree() is under feature mount and for Linux and Android, we should probably gate at_rawfd with:
#[cfg(any(
all(feature = "fs", not(target_os = "redox")),
all(
any(feature = "process", feature = "mount"),
any(target_os = "android", target_os = "linux")
)
))]
pub(crate) fn at_rawfd(fd: Option<RawFd>) -> raw::c_int {
fd.unwrap_or(libc::AT_FDCWD)
}| /// If target is a symbolic link, do not dereference it. | ||
| AT_SYMLINK_NOFOLLOW as c_uint; | ||
| /// Clone the mount object. | ||
| OPEN_TREE_CLONE as c_uint; |
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Is this cast necessary, it seems that this constant is of type c_uint on both Linux and Android:
$ rg "OPEN_TREE_CLONE"
src/unix/linux_like/android/mod.rs
2174:pub const OPEN_TREE_CLONE: ::c_uint = 0x01;
src/unix/linux_like/linux/mod.rs
3328:pub const OPEN_TREE_CLONE: ::c_uint = 0x01;
libc-test/semver/linux.txt
1728:OPEN_TREE_CLONE
libc-test/semver/android.txt
1754:OPEN_TREE_CLONEThere was a problem hiding this comment.
To support both Linux and Android, we use the following alias, for more detail, see cfg-gates
#[cfg(linux_android)]
| /// Clone the mount object. | ||
| OPEN_TREE_CLONE as c_uint; | ||
| /// Set the close-on-exec flag for the returned file descriptor. | ||
| OPEN_TREE_CLOEXEC as c_uint; |
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Same to this one:
$ rg "OPEN_TREE_CLOEXEC"
libc-test/semver/linux.txt
1727:OPEN_TREE_CLOEXEC
libc-test/semver/android.txt
1753:OPEN_TREE_CLOEXEC
src/unix/linux_like/linux/mod.rs
3329:pub const OPEN_TREE_CLOEXEC: ::c_uint = O_CLOEXEC as ::c_uint;
src/unix/linux_like/android/mod.rs
2175:pub const OPEN_TREE_CLOEXEC: ::c_uint = O_CLOEXEC as ::c_uint;| @@ -203,6 +204,31 @@ exit 23"; | |||
| assert_eq!(buf, SCRIPT_CONTENTS); | |||
| } | |||
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| pub(crate) fn test_open_tree() { | |||
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Nit: would like to change this to pub fn test_open_tree() so that it could be consistent with the other functions in this module :)
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Gentle on the author @lucab, would you like to finish this PR:) |
This adds an ergonomic wrapper for the Linux-specific
open_tree(2)syscall, using safe-io file descriptors.
The syscall has been introduced in kernel version 5.2 and allows
FD-based manipulation of mount hierarchies.