Date: Tue, 4 Apr 2000 22:29:29 +1000 (EST) From: Bruce Evans <bde@zeta.org.au> To: Poul-Henning Kamp <phk@critter.freebsd.dk> Cc: "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: <Pine.BSF.4.21.0004042139060.2001-100000@alphplex.bde.org> In-Reply-To: <23861.954797317@critter.freebsd.dk>
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On Mon, 3 Apr 2000, Poul-Henning Kamp wrote: > In message <Pine.BSF.4.21.0004040649300.1047-100000@alphplex.bde.org>, Bruce Ev > ans writes: > >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). > Uhm Bruce, the code to implement this dual valid bit thingie will take > up more space than we will ever save by doing it. > > Lets keep it simple please. You don't understand. This _is_ simple and efficient. See the first 40 lines of dscheck() which deal with translation from a logical blkno to slice-relative physical blkno. The duality bit handling adds only about 28 lines to this: if (ssp->dss_secmult == 1) { /* old */ if (biop->bio_flags & BIO_BYTEOFFSET) { if (biop->bio_offset % (u_int64_t)DEV_BSIZE) goto bad_bio_offset; if (biop->bio_offset >= (u_int64_t)DEV_BSIZE << 31) goto bad_bio_offset; secno = biop->b_offset >> DEV_BSHIFT; } else secno = blkno; /* old */ ... /* old */ } else { /* old */ and 2 more sets of 7 new lines for the other 2 special cases for ssp->dss_secmult, and 7 new lines for error reporting. The few callers that want a byte offset need 1 new line to set BIO_BYTEOFFSET. Currently, only physio() wants this. > I will propose we stick to just one field in struct bio: a 64bit > byte offset, we may want to keep a blkno around in struct buf, > but lets decide that separately. This requires more widespread changes to convert block numbers to offsets in all file systems, and normally gives 2 extra sets of conversions: first to offsets in the file systems, then to sector numbers in dscheck(). With more work on the filesystems, some of the conversions can be combined. E.g., in ffs, fs->fsbtodb gives the shift count for converting fs-blocks to "disk" blocks. It needs to be replaced by (fs->fsbtodb + 9) to convert directly from fs-blocks to byte offsets. Bruce To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe cvs-all" in the body of the message
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