From: Omar Sandoval <redacted>
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 a dcache helper for filesystem implementations of
AT_REPLACE. I'm not entirely convinced that it's 100% correct.
Patch 3 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.
Any comments are welcome.
Cc: Xi Wang <redacted>
Omar Sandoval (3):
fs: add AT_REPLACE flag for linkat() which replaces the target
vfs: add d_replace()
Btrfs: add support for linkat() AT_REPLACE
fs/btrfs/inode.c | 59 ++++++++++++++-
fs/dcache.c | 68 +++++++++++++++--
fs/ecryptfs/inode.c | 2 +-
fs/namei.c | 180 +++++++++++++++++++++++++++++++++++----------
fs/nfsd/vfs.c | 2 +-
fs/overlayfs/overlayfs.h | 2 +-
include/linux/dcache.h | 1 +
include/linux/fs.h | 3 +-
include/uapi/linux/fcntl.h | 1 +
9 files changed, 267 insertions(+), 51 deletions(-)
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2.10.2