On 10/22/20 5:22 PM, Matthew Wilcox wrote:

I'm working on making readpage synchronous so that it can actually return
errors instead of futilely setting PageError.  Something that's common
between most of the block based filesystems is the need to submit N
I/Os and wait for them to all complete (some filesystems don't support
sub-page block size, so they don't have this problem).

I ended up coming up with a fairly nice data structure which I've called
the blk_completion.  It waits for 'n' events to happen, then wakes the
task that cares, unless the task has got bored and wandered off to do
something else.

block_read_full_page() then uses this data structure to submit 'n' buffer
heads and wait for them to all complete.  The fscrypt code doesn't work
in this scheme, so I bailed on that for now.  I have ideas for fixing it,
but they can wait.

Obviously this all needs documentation, but I'd like feedback on the
idea before I do that.  I have given it some light testing, but there
aren't too many filesystems left that use block_read_full_page() so I
haven't done a proper xfstests run.

Hmm. You are aware, of course, that hch et al are working on replacing 
bhs with iomap, right?
So wouldn't it be more useful to concentrate on the iomap code, and 
ensure that _that_ is working correctly?

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                Kernel Storage Architect
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