On Fri, 2020-02-07 at 12:04 -0500, Jeff Layton wrote: > You're probably wondering -- Where are v1 and v2 sets? > > I did the first couple of versions of this set back in 2018, and then > got dragged off to work on other things. I'd like to resurrect this set > though, as I think it's valuable overall, and I have need of it for some > other work I'm doing. > > 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 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, and a new ioctl is added to allow > userland to get at the current errseq_t value w/o having to sync out > anything. > > I do have a xfstest for this. I do not yet have manpage patches, but > I'm happy to roll some once there is consensus on the interface. > > Caveats: > > - Having different behavior for an O_PATH descriptor in syncfs is > a bit odd, but it means that we don't have to grow struct file. Is > that acceptable from an API standpoint? > There are a couple of other options besides requiring an O_PATH fd here: 1) we could just add a new errseq_t field to struct file for this. On my machine (x86_64) there is 4 bytes of padding at the end of struct file. An errseq_t would slot in there without changing the slab object size. YMMV on other arches of course. 2) we could add a new fcntl command value (F_SYNCFS or something?), that would flip the fd to being suitable for syncfs. If you tried to use the fd to do a fsync at that point, we could return an error. Anyone else have other thoughts on how best to do this? > - This adds a new generic fs ioctl to allow userland to scrape the > current superblock's errseq_t value. It may be best to present this > to userland via fsinfo() instead (once that's merged). I'm fine with > dropping the last patch for now and reworking it for fsinfo if so. > To be clear, as I stated in earlier replies, I think we can drop the ioctl. If we did want something like this, I think we'd want to expose it via fsinfo() instead, and that could be done after the syncfs changes went in. > Jeff Layton (3): > vfs: track per-sb writeback errors and report them to syncfs > buffer: record blockdev write errors in super_block that it backs > vfs: add a new ioctl for fetching the superblock's errseq_t > > fs/buffer.c | 2 ++ > fs/ioctl.c | 4 ++++ > fs/open.c | 6 +++--- > fs/sync.c | 9 ++++++++- > include/linux/errseq.h | 1 + > include/linux/fs.h | 3 +++ > include/linux/pagemap.h | 5 ++++- > include/uapi/linux/fs.h | 1 + > lib/errseq.c | 33 +++++++++++++++++++++++++++++++-- > 9 files changed, 57 insertions(+), 7 deletions(-) > -- Jeff Layton <jlayton@xxxxxxxxxx>
