Am 30.01.2020 um 11:40 hat Vladimir Sementsov-Ogievskiy geschrieben: > 29.01.2020 21:01, Vladimir Sementsov-Ogievskiy wrote: > > Hi! > > > > I found a crash, which may be simply triggered for images unaligned to > > request_alignment: > > > > # ./qemu-io --image-opts -c 'write 0 512' > > driver=blkdebug,align=4096,image.driver=null-co,image.size=512 > > qemu-io: block/io.c:1505: bdrv_aligned_pwritev: Assertion `end_sector <= > > bs->total_sectors || child->perm & BLK_PERM_RESIZE' failed. > > Aborted (core dumped) > > > > The problem is obvious: 512 is aligned to 4096 and becomes larger than file > > size. > > > > I faced it after rebasing our downstream branches to newer Rhel versions. > > Seems that after some updates of alignment detection in file-posix.c, it > > started to detect 4096 alignment in our build environment, and iotest 152 > > started to crash (as it operates on file of 512 bytes). > > > > My question is: > > > > What is wrong? Should we restrict images to be aligned to > > request_alignment, or allow unaligned operations at EOF, if file is > > unaligned itself? > > > > > The problem started with commit > > commit a6b257a08e3d72219f03e461a52152672fec0612 > Author: Nir Soffer <[email protected]> > Date: Tue Aug 13 21:21:03 2019 +0300 > > file-posix: Handle undetectable alignment > > > It sets request_alignment to 4k, if probing of align=1 succeeded.. I think > it's wrong logic. It leads to crashes for images unaligned to 4k. > > If we force alignment to be 4k, we at least should check that file size is > aligned to 4k. Otherwise our assumption is definitely wrong. > > And still, I doubt that it's correct to force alignment to 4k, for devices > which doesn't request any alignment..
What backend is this? O_DIRECT with byte alignment sounds wrong, so I wonder if your storage really can do this or whether we just failed to detect the actual alignment. I guess we could change the default to pick the largest size so that the image size is still a multiple of it. But if the image size isn't even aligned to 512 bytes, I think refusing to open the image with O_DIRECT feels more correct (I would be okay with doing the same with > 512 byte images, too, if the image size isn't a multiple of the alignment). Kevin
