From: Omar Sandoval <osandov@xxxxxx> The goal of this series is to allow for updating a file atomically in-place with an O_TMPFILE like so: - open temporary file with O_TMPFILE - write temporary file contents - fsync temporary file - atomically replace permanent location with the temporary file This series implements atomic replace step with a new linkat(..., AT_REPLACE). Al, I took a look at implementing this usecase with renameat2() after we talked. Like you said, on the dcache side, "replace with tmpfile" looks a lot like rename. However, on the filesystem side, trying to use rename for this is much uglier than using link. We can't give i_op->rename() a meaningful old_dir, and dealing with that new special case gets messy fast. So, here is the approach of having AT_REPLACE just unhash the replaced dentry. >From the original cover letter: This is a proof-of-concept patch series implementing an AT_REPLACE flag for linkat(2) which allows us to replace the target. This is a nice primitive on its own, but it's most interesting when combined with O_TMPFILE, as it allows you to do an atomic update of a file with an O_TMPFILE. Patch 1 implements the VFS support for this flag. The implementation resembles sys_renameat2(), and I took care to preserve all of the original error cases and make the new error cases consistent with rename. Patch 2 adds support for AT_REPLACE to Btrfs. That's the codebase I'm most familiar with so that's where I started, but it should be straightforward to implement for other filesystems. Cc: Xi Wang <xi@xxxxxxxxxxxxxxxxx> Omar Sandoval (2): fs: add AT_REPLACE flag for linkat() which replaces the target Btrfs: add support for linkat() AT_REPLACE fs/btrfs/inode.c | 65 +++++++++++++++- fs/ecryptfs/inode.c | 2 +- fs/namei.c | 181 ++++++++++++++++++++++++++++++++++++--------- fs/nfsd/vfs.c | 2 +- fs/overlayfs/overlayfs.h | 2 +- include/linux/fs.h | 3 +- include/uapi/linux/fcntl.h | 1 + 7 files changed, 211 insertions(+), 45 deletions(-) -- 2.12.0
