Re: [PATCH v5 00/17] fs: introduce new writeback error reporting and convert ext2 and ext4 to use it

[Ross Zwisler]

On Wed, May 31, 2017 at 08:45:23AM -0400, Jeff Layton wrote:
> v5: don't retrofit old API over the new infrastructure
>     add fstype flag to indicate how wb errors are tracked within that fs
>     add more function variants that take a errseq_t "since" value
>     add second errseq_t to struct file to track metadata wb errors
>     convert ext4 and ext2 to use the new APIs
> 
> v4: several more cleanup patches
>     documentation and kerneldoc comment updates
>     fix bugs in gfs2 patches
>     make sync_file_range use same error reporting semantics
>     bugfixes in buffer.c
>     convert nfs to new scheme (maybe bogus, can be dropped)
> 
> v3: wb_err_t -> errseq_t conversion
>     clean up places that re-set errors after calling filemap_* functions
> 
> v2: introduce wb_err_t, use atomics
> 
> This is v5 of the patchset to improve how we're tracking and reporting
> errors that occur during pagecache writeback. The main difference in
> this set from the last one is that I've stopped trying to retrofit the
> old error tracking API on top of the new one. This is more work since
> we'll have to touch each fs individually, but should be safer as the
> "since" values used for checking errors will be more deliberate.
> 
> There are several situations where the kernel can "lose" errors that
> occur during writeback, such that fsync will return success even
> though it failed to write back some data previously. The basic idea
> here is to have the kernel be more deliberate about the point from
> which errors are checked to ensure that that doesn't happen.
> 
> An additional aim of this set is to change the behavior of fsync in
> Linux to report writeback errors on all fds instead of just the first
> one. This allows writers to reliably tell whether their data made it to
> the backing device without having to coordinate fsync calls with other
> writers.
> 
> To do this, we add a new typedef: errseq_t. This is a 32-bit value
> that can store an error code, and a sequence number so we can tell
> whether it has changed since we last sampled it. This allows us to
> record errors in the address_space and then report those errors only
> once per file description.
> 
> This set just alters block device files, ext4 and the legacy ext2
> driver. If this general approach seems acceptable, then I'll start
> converting other filesystems in follow-on patchsets. I'd also like
> to get this into linux-next as soon as possible to ensure that we're
> banging out any bugs that might be lurking here.
> 
> I also have a couple of xfstests for this as well that I'll re-post
> soon.

Can you tell me a baseline that this applies cleanly to, or give me a link to
a tree with these patches already applied?  I've tried applying it to v4.11,
linux/master and mmots/master, and so far nothing has worked.