On Tue, Oct 08, 2013 at 04:56:23PM +0100, Pádraig Brady wrote: > For my own reference, the way I see it, > when accessing block devices Linux uses these block sizes: > > physical defined by the hardware device > logical the smallest addressable unit used for the device > file system ditto for the file system > > --[gs]etbsz refers the _logical_ block size for the device. Well, let's be more pedantic ;-) The disks and raids provides I/O limits: physical block size (BLKPBSZGET) logical block size (BLKSSZGET) but kernel also uses soft block size BLKBSZGET this size is never smaller than logical size and (I guess) usually same as PAGE_SIZE. So it's really not *device* logical block size, it's more about the way how kernel uses the device. > So why might one want to --setbsz? > I agree that would be fairly specialized. Yes, it's practically useless in tool like blockdev(8). > I searched for uses of --setbz and noticed a couple: > Perf testing: > https://lkml.org/lkml/2003/12/30/81 > Functionality testing: > http://www.linux-archive.org/device-mapper-development/699549-blockdev-fix-crash-when-block-size-changed-i-o-issued-simultaneously.html Good point (it seems I was too rash to apply Rich's patch;-) Maybe we can keep --setbsz in the code for testing purpose and for backward compatibility, then all we need is describe the ioctl in the blockdev(8) man page. Karel -- Karel Zak <kzak@xxxxxxxxxx> http://karelzak.blogspot.com -- To unsubscribe from this list: send the line "unsubscribe util-linux" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
