Re: [Libguestfs] [RFC] lib: allow to specify physical/logical block size for disks

пн, 10 лют. 2020 о 13:43 Richard W.M. Jones <rjones(a)redhat.com&gt; пише: > > On Sat, Feb 08, 2020 at 01:25:28AM +0200, Mykola Ivanets wrote: > > From: Nikolay Ivanets <stenavin(a)gmail.com&gt; > > > > I faced with situation where libguestfs cannot recognize partitions on a > > disk image which was partitioned on a system with "4K native" sector > > size support. > > Do you have a small test case for this? We can easily create one with patched libguestfs and attach disk to unpatched libguestfs. > > In order to fix the issue we need to allow users to specify desired > > physical and/or logical block size per drive basis. > > It seems like physical_block_size / logical_block_size in qemu are > completely undocumented. However I did some experiments with patching > libguestfs and examining the qemu and parted code. Here are my > observations: > > (1) Setting only physical_block_size = 4096 seems to do nothing. See my thoughts on this in previous email. > (2) Setting only logical_block_size = 4096 is explicitly rejected by > virtio-scsi: > > https://git.qemu.org/?p=qemu.git;a=blob;f=hw/scsi/scsi-disk.c;h=10d0794d6... > > (A similar test exists for virtio-blk) > > (3) Setting both physical_block_size = logical_block_size = 4096 > changes how parted partitions GPT disks. The partition table is > clearly using 4K sectors as you can see by examining the disk > afterwards with hexdump. > > (4) Neither setting changes MBR partitioning by parted, although my > interpretation of Wikipedia indicates that it should be possible to > create a MBR disk with 4K sector size. Maybe I'm doing something > wrong, or parted just doesn't support this case. > > So it appears that we should just have one blocksize control (maybe > called "sectorsize"?) which sets both physical_block_size and > logical_block_size to the same value. It may also be worth enforcing > that blocksize/sectorsize must be set to 512 or 4096 (which we can > relax later if necessary). If we stick with the only parameter, I think blocksize might be better name, especially if we want to split this parameter somewhere latter. Here are more precise restrictions: Both values must be a power of 2 between 512 and 32768. logical_block_size must be less or equals to physical_block_size.