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fs: link fallback for atomic create

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Some file systems don't support renameat2's RENAME_NOREPLACE
flag (eg. ZFS), at the some time, some other file systems
don't support hardlinks via link (eg. vfat, cifs), so we now
try both: first the rename (since it's more efficient), then
link+unlink for the rest.

If both fail, the file system is simply not supported for
our purposes anyway...

Signed-off-by: Wolfgang Bumiller <w.bumiller@proxmox.com>
This commit is contained in:
Wolfgang Bumiller 2021-07-22 09:33:19 +02:00 committed by Thomas Lamprecht
parent 2d9a018854
commit 11dccc40b5
1 changed files with 11 additions and 3 deletions
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14
proxmox/src/tools/fs.rs
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@ -236,14 +236,22 @@ pub fn atomic_open_or_create_file<P: AsRef<Path>>(
// the initialization, the first one wins!
let rename_result = temp_file_name.with_nix_path(|c_file_name| {
path.with_nix_path(|new_path| unsafe {
let rc = libc::renameat2(
// This also works on file systems which don't support hardlinks (eg. vfat)
match Errno::result(libc::renameat2(
libc::AT_FDCWD,
c_file_name.as_ptr(),
libc::AT_FDCWD,
new_path.as_ptr(),
libc::RENAME_NOREPLACE,
);
nix::errno::Errno::result(rc)
)) {
Err(nix::Error::Sys(Errno::EINVAL)) => (), // dumb file system, try `link`+`unlink`
other => return other,
};
// but some file systems don't support `RENAME_NOREPLACE`
// so we just use `link` + `unlink` instead
let result = Errno::result(libc::link(c_file_name.as_ptr(), new_path.as_ptr()));
let _ = libc::unlink(c_file_name.as_ptr());
result
})
});