-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 On Sat, Mar 24, 2007 at 09:51:04PM +0200, Tzahi Fadida wrote: > I am reading from LDD3 and in the block device chapter there is a talk about > KERNEL_SECTOR_SIZE which is supposed to be 512bytes. > The problem is the terminology. A sector is a very big thing, i.e.: > in a floppy you have 18 sectors, 2 heads, 80 cylinders and a block size of > 512bytes. The size of a sector (which is a slice) is 80 * 512 bytes. > http://en.wikipedia.org/wiki/Cylinder-head-sector > I am sure this is not what they meant in the kernel. > I.e., i think they meant block size. A sector is the smallest addressable entity on a disk. Almost all hard drives have 512 byte sectors, though SCSI drives can be reformated with a different sector size (512 to up to 524 bytes IIRC). Hard drives with 1k sector sizes will become available in the near future. > but in the same code they also mention a sector which seems to be referring to > the number of sectors:16 (slice). In section 16.2.3 > And then they say geo.start = 4 to refer to the starting sector but this time > again they probably mean block. This is confusing. Can somebody clear this > up? > > Also, regarding sectors of 2048 bytes (block size) and the kernel works with > 512bytes. If your device work in 2048 bytes, do you have to translate each > sector (block) to 4 consecutive kernel sectors in the (virtual) array of > sectors the kernel sees in your driver? See how the SCSI CD driver works (drivers/scsi/sr.c), CDs usually have a 2k sector size. > The problem with that is that it would think that a request are not on the > same cylinder and won't group it correctly. I.e. 4 virtual kernel cylinders > are actually 1 cylinder in the device. AFAIU the kernel takes care of that when it is told that a device has a 2k sector size. Erik - -- They're all fools. Don't worry. Darwin may be slow, but he'll eventually get them. -- Matthew Lammers in alt.sysadmin.recovery -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.6 (GNU/Linux) iD8DBQFGB7kt/PlVHJtIto0RAqdMAJ98pHEH0PJ8/kXtCVyxzM4N3m8cVACfc3iV 3ExVFXwwH4Yy7/NMsPkHz4M= =cKow -----END PGP SIGNATURE----- -- To unsubscribe from this list: send an email with "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx Please read the FAQ at http://kernelnewbies.org/FAQ
