[Adding linux-ext4 mailing list. The original bug report is here: https://www.redhat.com/archives/libguestfs/2015-November/msg00078.html ] On Sat, Nov 07, 2015 at 01:22:45PM -0600, Jason Pepas wrote: > On Sat, Nov 7, 2015 at 5:03 AM, Richard W.M. Jones <rjones@xxxxxxxxxx> wrote: > > How about 'strace mkfs.ext2 ..' and see if any system calls are > > returning errors. That would show you whether nbd-client is throwing > > errors away, or whether mkfs is getting the errors and ignoring them > > (seems pretty unlikely, but you never know). > > > > After that, it'd be down to tracing where the errors end up in the > > kernel. > > Thanks for the tip! > > The results are interesting. It looks like all of mkfs's pwrite() > calls succeed, but its final fsync() calls do actually fail: > > > root@debian:~# strace mkfs.ext2 /dev/nbd0 2>&1 | tee strace.out > > root@debian:~# cat strace.out | grep pwrite > pwrite(3, "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., > 32768, 8187379712) = 32768 > pwrite(3, "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., > 32768, 8187412480) = 32768 > pwrite(3, "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., > 32768, 8187445248) = 32768 > ... > > root@debian:~# cat strace.out | grep fsync > fsync(3) = -1 EIO (Input/output error) > fsync(3) = -1 EIO (Input/output error) > > > The fsync() calls happen just before mkfs exists success: > > > root@debian:~# cat strace.out | tail > pwrite(3, "\1\2\0\0\2\2\0\0\3\2\0\0\367{\365\37\2\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., > 4096, 6576672768) = 4096 > fsync(3) = -1 EIO (Input/output error) > pwrite(3, "\0\0\10\0\0\0 > \0\231\231\1\0qm\37\0\365\377\7\0\0\0\0\0\2\0\0\0\2\0\0\0"..., 1024, > 1024) = 1024 > fsync(3) = -1 EIO (Input/output error) > close(3) = 0 > write(1, "done\n\n", 6done > > ) = 6 > exit_group(0) = ? > +++ exited with 0 +++ > root@debian:~# > > > I did manage to find two calls to fsync in the e2fsprogs source which > are not return-value-checked: > > https://github.com/tytso/e2fsprogs/blob/956b0f18a5ddb6815a9dff4f10a1e3125cdca9ba/misc/filefrag.c#L303 > https://github.com/tytso/e2fsprogs/blob/956b0f18a5ddb6815a9dff4f10a1e3125cdca9ba/lib/ext2fs/unix_io.c#L915 That second one looks very suspicious to me. I don't think that it's ever right for mke2fs to ignore the return value from an fsync call, so assuming mke2fs calls that function it's surely a bug. > I'll see about submitting a patch there. > > I'm not sure where to start with hunting down why mkfs's pwrite() > calls aren't failing. I'd look to the kernel source for that? It looks like it's really an e2fsprogs problem, not a kernel problem. That's pretty surprising - I wasn't expecting it. Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com virt-p2v converts physical machines to virtual machines. Boot with a live CD or over the network (PXE) and turn machines into KVM guests. http://libguestfs.org/virt-v2v -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
