Messages in this thread | | | Subject | Re: [PATCH 0/2] block layer filter and block device snapshot module | From | Hannes Reinecke <> | Date | Fri, 23 Oct 2020 12:31:05 +0200 |
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On 10/23/20 11:13 AM, hch@infradead.org wrote: > On Thu, Oct 22, 2020 at 01:54:16PM -0400, Mike Snitzer wrote: >> On Thu, Oct 22, 2020 at 11:14 AM Darrick J. Wong >>> Stupid question: Why don't you change the block layer to make it >>> possible to insert device mapper devices after the blockdev has been set >>> up? >> >> Not a stupid question. Definitely something that us DM developers >> have wanted to do for a while. Devil is in the details but it is the >> right way forward. >> > > Yes, I think that is the right thing to do. And I don't think it should > be all that hard. All we'd need in the I/O path is something like the > pseudo-patch below, which will allow the interposer driver to resubmit > bios using submit_bio_noacct as long as the driver sets BIO_INTERPOSED. > > diff --git a/block/blk-core.c b/block/blk-core.c > index ac00d2fa4eb48d..3f6f1eb565e0a8 100644 > --- a/block/blk-core.c > +++ b/block/blk-core.c > @@ -1051,6 +1051,9 @@ blk_qc_t submit_bio_noacct(struct bio *bio) > return BLK_QC_T_NONE; > } > > + if (blk_has_interposer(bio->bi_disk) && > + !(bio->bi_flags & BIO_INTERPOSED)) > + return __submit_bio_interposed(bio); > if (!bio->bi_disk->fops->submit_bio) > return __submit_bio_noacct_mq(bio); > return __submit_bio_noacct(bio); > My thoughts went more into the direction of hooking into ->submit_bio, seeing that it's a NULL pointer for most (all?) block drivers.
But sure, I'll check how the interposer approach would turn out.
Cheers,
Hannes -- Dr. Hannes Reinecke Kernel Storage Architect hare@suse.de +49 911 74053 688 SUSE Software Solutions GmbH, Maxfeldstr. 5, 90409 Nürnberg HRB 36809 (AG Nürnberg), Geschäftsführer: Felix Imendörffer
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