Re: [PATCH] squashfs: Migrate from ll_rw_block usage to BIO

[Christoph Hellwig]

On Wed, Oct 30, 2019 at 10:19:54AM +0900, Philippe Liard wrote:
> > What access do you need to synchronize?  If you read data into the
> > page cache the page lock provides all synchronization needed.  If
> > you just read into decrompression buffers there probably is no need
> > for synchronization at all as each buffer is only accessed by one
> > thread at a time.
> My main concern here was waiting for the BIO request to complete but
> submit_bio_wait() that you pointed out below should address that.

Note that if you are doing multiple bios for a single request using
submit_bio_wait might not be optimal.  In that case you probably want
a refcount and only complete when all of them are done, but by looking
at submit_bio_wait should get an idea how that works.  Alternatively look
at others users, e.g. __blkdev_direct_IO in fs/block_dev.c that already
support multiple bios.