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From: Jasper Surmont <surmontjasper@gmail.com>
To: linux-block@vger.kernel.org
Subject: [Question] Accessing read data in bio request
Date: Thu, 14 Apr 2022 17:15:31 +0300	[thread overview]
Message-ID: <CAH4tiUtGuZP6QnO6L9EEDFL08O-UusHihO6CbvEf-QwJM3QPCg@mail.gmail.com> (raw)

I'm writing a device mapper target, and on a bio (read) request I want
to access (for example just logging) the data that was just read (by
providing a callback to bio->bio_end_io).

I've figured out I could read the data by using bvec_kmap_local() on
each bio_vec to get a pointer to the data. However, if my
understanding is correct this seems like an unefficient way: if the
bio just finished a read then shouldn't the data already be mapped
somewhere? If so, where?

2nd question: using bio_for_each_segment(...) inside the bio_end_io
callback never loops. Is this normal, and if so why?

Thanks!

             reply	other threads:[~2022-04-14 15:07 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-04-14 14:15 Jasper Surmont [this message]
2022-04-18  1:59 ` [Question] Accessing read data in bio request Jens Axboe
2022-04-18 13:06   ` Jasper Surmont
2022-04-18 15:33     ` Jens Axboe

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