• Jeff Layton's avatar
    vfs: track per-sb writeback errors and report them to syncfs · 735e4ae5
    Jeff Layton authored
    Patch series "vfs: have syncfs() return error when there are writeback
    errors", v6.
    
    Currently, syncfs does not return errors when one of the inodes fails to
    be written back.  It will return errors based on the legacy AS_EIO and
    AS_ENOSPC flags when syncing out the block device fails, but that's not
    particularly helpful for filesystems that aren't backed by a blockdev.
    It's also possible for a stray sync to lose those errors.
    
    The basic idea in this set is to track writeback errors at the
    superblock level, so that we can quickly and easily check whether
    something bad happened without having to fsync each file individually.
    syncfs is then changed to reliably report writeback errors after they
    occur, much in the same fashion as fsync does now.
    
    This patch (of 2):
    
    Usually we suggest that applications call fsync when they want to ensure
    that all data written to the file has made it to the backing store, but
    that can be inefficient when there are a lot of open files.
    
    Calling syncfs on the filesystem can be more efficient in some
    situations, but the error reporting doesn't currently work the way most
    people expect.  If a single inode on a filesystem reports a writeback
    error, syncfs won't necessarily return an error.  syncfs only returns an
    error if __sync_blockdev fails, and on some filesystems that's a no-op.
    
    It would be better if syncfs reported an error if there were any
    writeback failures.  Then applications could call syncfs to see if there
    are any errors on any open files, and could then call fsync on all of
    the other descriptors to figure out which one failed.
    
    This patch adds a new errseq_t to struct super_block, and has
    mapping_set_error also record writeback errors there.
    
    To report those errors, we also need to keep an errseq_t in struct file
    to act as a cursor.  This patch adds a dedicated field for that purpose,
    which slots nicely into 4 bytes of padding at the end of struct file on
    x86_64.
    
    An earlier version of this patch used an O_PATH file descriptor to cue
    the kernel that the open file should track the superblock error and not
    the inode's writeback error.
    
    I think that API is just too weird though.  This is simpler and should
    make syncfs error reporting "just work" even if someone is multiplexing
    fsync and syncfs on the same fds.
    Signed-off-by: default avatarJeff Layton <jlayton@kernel.org>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Reviewed-by: default avatarJan Kara <jack@suse.cz>
    Cc: Andres Freund <andres@anarazel.de>
    Cc: Matthew Wilcox <willy@infradead.org>
    Cc: Al Viro <viro@zeniv.linux.org.uk>
    Cc: Christoph Hellwig <hch@infradead.org>
    Cc: Dave Chinner <david@fromorbit.com>
    Cc: David Howells <dhowells@redhat.com>
    Link: http://lkml.kernel.org/r/20200428135155.19223-1-jlayton@kernel.org
    Link: http://lkml.kernel.org/r/20200428135155.19223-2-jlayton@kernel.orgSigned-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    735e4ae5
sync.c 10.5 KB