What were you trying to do that didn't work?

While trying to create a filesystem on a file, located on an ext4 filesystem, with a required alignment of 4 KiB, mkfs.xfs fails to read/write due to performing O_DIRECT IO using a 512-byte aligned buffer.

Please provide the package NVR for which bug is seen:

xfsprogs 4.5.0-22.el7.s390x

How reproducible:

always on customer's s390x system; unclear on other systems

Steps to reproduce

on device requiring 4 KiB alignment:

1. create ext4 filesystem
2. mount ext4 filesystem (mount /dev/... /mnt)
3. try to create xfs filesystem on a file on the ext4 filesystem

if the ext4 filesystem is itself a file on a filesystem, the 4 KiB alignment requirement may be forced when calling losetup:

1. losetup -b 4096 --find --show foo.ext4
   /dev/loop4

however, it's unclear how to cause the memalign() to align to just 512 bytes; it tends to also be aligned to 4 KiB (at least on x86_64)

Expected results

mkfs.xfs creates filesystem

Actual results

existing superblock re__memalign_hookad failed: Invalid argument
mkfs.xfs: pwrite64 failed: Invalid argument

the problem is in platform_findsizes() when creating the filesystem on a file:

        if ((st.st_mode & S_IFMT) == S_IFREG) {
                struct dioattr  da;
                *sz = (long long)(st.st_size >> 9);
                if (ioctl(fd, XFS_IOC_DIOINFO, &da) < 0) {
                        /*
                         * fall back to BBSIZE; mkfs might fail if there's a
                         * size mismatch between the image & the host fs...
                         */
                        *bsz = BBSIZE;                 }
                else
                        *bsz = da.d_miniosz;
                if (*bsz > max_block_alignment)
                        max_block_alignment = *bsz;
                return;
        } 

the ioctl fails on any non-xfs filesystem, so bsz is set to BBSIZE, which is 512 bytes.  In this case, the required alignment is 4096, so 512 bytes isn't sufficient.  Strace confirms that the buffer address is only aligned to 512 bytes:

1570 14:08:46.808737 pread64(16</var/lib/leapp/scratch/diskimages/root_>, 0x8ee49a00, 512, 0) = -1 EINVAL (Invalid argument) <0.000002> 

$ printf %x\\n $((0x8ee49a00 & 4095))
a00
$ printf %x\\n $((0x8ee49a00 & 511))
0
$ printf %x\\n $((0x8ee49a00 & 1023))
200 

in this case, the /var device is dm-3:

$ cat sos_commands/block/blockdev_--report
RO    RA   SSZ   BSZ   StartSec            Size   Device
rw  1024  4096  4096          0     23796449280   /dev/dasda
...
rw  8192  4096  4096          0     10712252416   /dev/dm-3