Re: [PATCH V18 00/18] Allow I/O on blocks whose size is less than page size

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On Tue, Apr 26, 2016 at 08:48:49PM +0530, Chandan Rajendra wrote:
> On Tuesday 26 Apr 2016 14:54:46 Filipe Manana wrote:
> 
> > Hi Chandan,
> > 
> > What does it mean the tests don't pass? Is there absolutely no code
> > changes for scrub and compression, or there is but still needs more
> > working, or what?
> >
> 
> Hi Filipe,
> 
> The patches that have been sent have no changes made with respect to either
> scrub or compression.
> 
> > What happens if, when one is using block size < page size, and enables
> > compression on a single file (i.e. fs not mounted with -o compress or
> > force-compress), we start writing and read to the file? Does it result
> > in the syscalls failing with -EIO or some other error, does it result
> > in crashes (BUG_ON(), etc), dues it result in transparently falling
> > back to non compression mode, or what happens exactly?
> 
> With the current patchset, reading/writing to a compressed file in
> (block size == page size) scenario works fine. However reading/writing to a
> compressed file in (block size < page size) results in crashes.

Lack of support for compression was pre-agreed but chrashes do not seem
ok to me, if there are EINVAL or EOPNOTSUPP erros that would be
acceptable for the first version I think. We will run fstests with this
patchset so if a test fails then we can see if it was due to
compression, but a crash would make testing tedious, manual test
exception needed etc.

> > Same kind of question regarding scrub.
> 
> Scrub works fine for (block size == page size) scenario. However, Scrub ioctl
> returns -EINVAL for the case where block size != page size. Without the block
> size check, scrub might result in crashes.

EINVAL should be ok here.
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