[PATCH 0/7] Configurable error behavior [V3]

[Carlos Maiolino]

On Thu, May 05, 2016 at 10:11:07AM -0400, Brian Foster wrote:
> On Wed, May 04, 2016 at 05:43:13PM +0200, Carlos Maiolino wrote:
> > This is the new revision of this patchset, according to last comments.
> > 
> > This patchset is aimed to implement a configurable error behavior in XFS, and
> > most of the design has been done by Dave, so, that's why I kept his signed-off
> > in the patches.
> > 
> > This new revision has the detailed changelog written on each patch, but the
> > major changes are:
> > 
> > 	- Detailed changelog by-patch and description fixed to become
> > 	  (hopefuly) more clear
> > 	- kept fail_at_unmount as a sysfs attribute
> > 
> > 
> > Regarding fail_at_unmount, I left it almost exactly as Dave's design, giving his
> > comments on the last revision, although, I still think there is no need to keep
> > it as a per-error granularity, so, I was wondering if a single, global option in
> > /sys/fs/xfs/<dev>/error/fail_at_unmount wouldn't suffice, but, this will require
> > a new place to store the value inside kernel, instead of keeping it inside
> > struct xfs_error_cfg, or maybe use the same structure but use it outside of the
> > m_error_cfg array?
> > 
> 
> I agree with regard to the granularity of fail_at_unmount. This was
> brought up previously:
> 
> http://oss.sgi.com/archives/xfs/2016-02/msg00558.html
> 
> ... and I haven't heard a use case for per-error granularity.

Hi, yes, my comment was based on our previous discussion, my apologies to not
have made it clear.

> 
> I suggest just to pull it out of the error classification stuff entirely
> and place it under xfs_mount. E.g., at the same level as "fail_writes"
> (but not a DEBUG mode only option).
> 
> I'm also wondering whether we need more mechanism for the
> fail_at_unmount behavior. For example, instead of defining
> XFS_MOUNT_UNMOUNTING, could we just call a function that resets
> max_retries (of each class) to 0 in the unmount path? Then maybe call
> the mount tunable retry_on_unmount or something like that. Thoughts?
> 
I don't oppose to that, although, having a flag like XFS_MOUNT_UNMOUNTING, might
be useful in the future, but still, wouldn't be better this single flag, instead
of walk through all classes/errors resetting the max_retries? It sounds as
granular as having fail_at_unmount inside each error, despite the fact it's not
exposed to user-space, we will need to interact over each max_retries to
actually shutdown the filesystem during unmount, which, is also error-prone
IMHO.
It also depends on how granular we will implement fail_at_unmount. If it's a
single global option, resetting all max_retries works, otherwise it might not
work, for example, if we decide to have fail_at_unmount for each class, we might
need to reset max_retries only in specific errors, which will increase the
complexity of the code.

Well, hope my comments make sense, just giving my $0.02 :)

cheers

> Brian
> 
> > First 6 patches are ready, the fail_at_unmount one, need to be re-worked if we
> > want it in a less granular way, but until now I don't think we reached any
> > decision about how it should be implemented.
> > 
> >  fs/xfs/xfs_buf.h      |  22 ++++
> >  fs/xfs/xfs_buf_item.c | 126 ++++++++++++++--------
> >  fs/xfs/xfs_mount.c    |  19 +++-
> >  fs/xfs/xfs_mount.h    |  32 ++++++
> >  fs/xfs/xfs_sysfs.c    | 283 +++++++++++++++++++++++++++++++++++++++++++++++++-
> >  fs/xfs/xfs_sysfs.h    |   3 +
> >  6 files changed, 437 insertions(+), 48 deletions(-)
> > 
> > -- 
> > 2.4.11
> > 
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-- 
Carlos