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If in the same transaction we rename a special file (fifo, character/block device or symbolic link), create a hard link for it having its old name then sync the log, we will end up with a log that can not be replayed and at when attempting to replay it, an EEXIST error is returned and mounting the filesystem fails. Example scenario: $ mkfs.btrfs -f /dev/sdc $ mount /dev/sdc /mnt $ mkdir /mnt/testdir $ mkfifo /mnt/testdir/foo # Make sure everything done so far is durably persisted. $ sync # Create some unrelated file and fsync it, this is just to create a log # tree. The file must be in the same directory as our special file. $ touch /mnt/testdir/f1 $ xfs_io -c "fsync" /mnt/testdir/f1 # Rename our special file and then create a hard link with its old name. $ mv /mnt/testdir/foo /mnt/testdir/bar $ ln /mnt/testdir/bar /mnt/testdir/foo # Create some other unrelated file and fsync it, this is just to persist # the log tree which was modified by the previous rename and link # operations. Alternatively we could have modified file f1 and fsync it. $ touch /mnt/f2 $ xfs_io -c "fsync" /mnt/f2 <power failure> $ mount /dev/sdc /mnt mount: mount /dev/sdc on /mnt failed: File exists This happens because when both the log tree and the subvolume's tree have an entry in the directory "testdir" with the same name, that is, there is one key (258 INODE_REF 257) in the subvolume tree and another one in the log tree (where 258 is the inode number of our special file and 257 is the inode for directory "testdir"). Only the data of those two keys differs, in the subvolume tree the index field for inode reference has a value of 3 while the log tree it has a value of 5. Because the same key exists in both trees, but have different index, the log replay fails with an -EEXIST error when attempting to replay the inode reference from the log tree. Fix this by setting the last_unlink_trans field of the inode (our special file) to the current transaction id when a hard link is created, as this forces logging the parent directory inode, solving the conflict at log replay time. A new generic test case for fstests was also submitted. Signed-off-by: Filipe Manana <fdmanana@suse.com> Signed-off-by: David Sterba <dsterba@suse.com> |
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README
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.