On Mon, Apr 11, 2022 at 11:06:17AM -0400, Douglas Gilbert wrote: > On 2022-04-11 01:03, Christoph Hellwig wrote: >> This still misses any good explanation of why we want all this. > > Advantages: > - undoes regression in ce70fd9a551af, that is: > - cdb_len > 32 no longer allowed (visible to the user space), undone What exact regression causes this for real users and no just people playing around with scsi_debug? > - but we still have this one: > - prior to lk5.18 sizeof(scsi_cmnd::cmnd) is that of a > pointer but >= lk5.18 sizeof(scsi_cmnd::cmnd) is 32 (or 16) Please check the total size of struct scsi_cmnd, which is what really matters. > - makes all scsi_cmnd objects 16 bytes smaller Do we have data why this matters? > - hides the poorly named dtor for scsi_cmnd objects (blk_mq_free_request) > within a more intuitively named inline: scsi_free_cmnd I don't think this is in any way poorly named. > Disadvantages: > - burdens each access to a CDB with (scsi_cmnd::flags & SCMD_LONG_CDB) > check > - LLDs that want to fetch 32 byte CDBs (or longer) need to use the > scsi_cmnd_get_cdb() access function. For CDB lengths <= 16 bytes > they can continue to access scsi_cmnd::cmnd directly It adds back the dynamic allocation for 32-byte CDBs that we got rid of. It also breaks all LLDS actually using 32-byte CDBS currently as far as I can tell.
