Re: [PATCH] fuse: update size attr before doing IO

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On 3/7/24 17:09, Josef Bacik wrote:
> On Thu, Mar 07, 2024 at 10:08:13AM -0500, Sweet Tea Dorminy wrote:
>> All calls into generic vfs functions need to make sure that the inode
>> attributes used by those functions are up to date, by calling
>> fuse_update_attributes() as appropriate.
>> generic_write_checks() accesses inode size in order to get the
>> appropriate file offset for files opened with O_APPEND. Currently, in
>> some cases, fuse_update_attributes() is not called before
>> generic_write_checks(), potentially resulting in corruption/overwrite of
>> previously appended data if i_size is out of date in the cached inode.
>> Therefore,  make sure fuse_update_attributes() is always
>> called before generic_write_checks(), and add a note about why it's not
>> necessary for some llseek calls.
>> Signed-off-by: Sweet Tea Dorminy <sweettea-kernel@xxxxxxxxxx>
> I had to ask questions and go look at the code, mostly because I'm not a FUSE
> developer.  fuse_update_attributes() doesn't actually do anything if the stats
> aren't invalidated, I was concerned we were suddenly adding a lot of overhead
> for every write call.

Unless the timeout is set to 0?

> Reviewed-by: Josef Bacik <josef@xxxxxxxxxxxxxx>
> I have a question for the normal FUSE developers, how would one test this?
> There doesn't appear to be a mechanism for writing stub FUSE fs's to exercise a
> case like this in fstests.  Is there some other way you guys would test this or
> is this something we need to build out ourselves?  Thanks,

You mean for xfstests? I'm testing fuse all the time with it.


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