Date: Mon, 3 Apr 2000 14:21:11 -0700 (PDT) From: Matthew Dillon <dillon@apollo.backplane.com> To: Bruce Evans <bde@zeta.org.au> Cc: Poul-Henning Kamp <phk@critter.freebsd.dk>, "Justin T. Gibbs" <gibbs@FreeBSD.ORG>, cvs-committers@FreeBSD.ORG, cvs-all@FreeBSD.ORG Subject: Re: cvs commit: src/sys/kern kern_mib.c vfs_bio.c src/sys/sys buf.h Message-ID: <200004032121.OAA61456@apollo.backplane.com> References: <Pine.BSF.4.21.0004040649300.1047-100000@alphplex.bde.org>
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:Not quite. Something obviously has to set the disk-level block number
:(currently bio_pblkno). It should be set from a valid block number or
:offset (bio_blkno or bio_offset). There needs to be a validity bit or
:out-of bounds values to indicate invalid fields (I prefer the bit).
:Callers prefer bio_blkno if it is convenient and works (i.e., in most
:cases, until 1TB disks become common).
:
:bio_offset could be overlayed with bio_blkno to save space (this requires
:a validity bit). The validity bit essentially gives a block size.
:It is set when the block size is 1 and the full 64 bits of the offset
:are valid, and clear when the block size is DEV_BSIZE and only 32 bits
:of the offset are valid.
:
:Bruce
This seems needlessly complex to me. A low level device driver knows
what the sector size of its physical media is, if we are going to mess
with the offset/blocknumber fields at all we should simply have a single
64 bit offset field. No validity bits, no dualities, no confusion
anywhere in the chain.
-Matt
Matthew Dillon
<dillon@backplane.com>
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