Re: [PULL 13/14] tests: Add iotest mirror-sparse for recent patches

[Fiona Ebner <f.ebner@proxmox.com>]

Hi,

Am 15.05.25 um 04:28 schrieb Eric Blake:
> +do_test full ignore off full

for me, this one fails irregularly (more than 50% of the time) with:
-Destination is full; expected full
+Destination is unknown; expected full

My file system is ext4 inside a virtual machine.
> [I] febner@dev8 ~/repos/qemu/build/tests/qemu-iotests (master) [1]> findmnt --target .
> TARGET             SOURCE   FSTYPE OPTIONS
> /home/febner/repos /dev/sdb ext4   rw,relatime

The virtual disk is an LVM image. When the test fails, I consistently
get 20975616 bytes rather than 20971520 bytes as the result of
disk_usage(), i.e. it has one 4 KiB block more. ls -l will still report
20971520 bytes as the length, qemu-img compare succeeds.

After the image creation, i.e. job1, the allocation is still as expected:
> +20971520	/home/febner/repos/qemu/build/tests/qemu-iotests/scratch/raw-file-mirror-sparse/t.raw
> +-rw-r--r-- 1 febner febner 20971520 May 21 11:18 /home/febner/repos/qemu/build/tests/qemu-iotests/scratch/raw-file-mirror-sparse/t.raw

Only after mirroring, i.e. job2, it will be larger:
> +20975616	/home/febner/repos/qemu/build/tests/qemu-iotests/scratch/raw-file-mirror-sparse/t.raw
> +-rw-r--r-- 1 febner febner 20971520 May 21 11:18 /home/febner/repos/qemu/build/tests/qemu-iotests/scratch/raw-file-mirror-sparse/t.raw

Some more information:

> [I] febner@dev8 ~/repos/qemu/tests/qemu-iotests/tests (master)> sudo filefrag /home/febner/repos/qemu/build/tests/qemu-iotests/scratch/raw-file-mirror-sparse/t.raw -e
> Filesystem type is: ef53
> File size of /home/febner/repos/qemu/build/tests/qemu-iotests/scratch/raw-file-mirror-sparse/t.raw is 20971520 (5120 blocks of 4096 bytes)
>  ext:     logical_offset:        physical_offset: length:   expected: flags:
>    0:        0..      15:   36233216..  36233231:     16:            
>    1:       16..    2047:   36233232..  36235263:   2032:             unwritten
>    2:     2048..    2559:   36239360..  36239871:    512:   36235264:
>    3:     2560..    4095:   36239872..  36241407:   1536:             unwritten
>    4:     4096..    5119:   33792000..  33793023:   1024:   36241408: last,unwritten,eof
> /home/febner/repos/qemu/build/tests/qemu-iotests/scratch/raw-file-mirror-sparse/t.raw: 3 extents found

Note that one of the offsets is not 4KiB-aligned:
> 36239360%4096
> 2048

I suppose that is the reason?

> [I] febner@dev8 ~/repos/qemu/tests/qemu-iotests/tests (master)> stat /home/febner/repos/qemu/build/tests/qemu-iotests/scratch/raw-file-mirror-sparse/t.raw
>   File: /home/febner/repos/qemu/build/tests/qemu-iotests/scratch/raw-file-mirror-sparse/t.raw
>   Size: 20971520  	Blocks: 40968      IO Block: 4096   regular file
> Device: 8,16	Inode: 4866541     Links: 1
> Access: (0644/-rw-r--r--)  Uid: ( 1000/  febner)   Gid: ( 1000/  febner)
> Access: 2025-05-21 11:18:37.622692254 +0200
> Modify: 2025-05-21 11:18:37.540686997 +0200
> Change: 2025-05-21 11:18:37.540686997 +0200
>  Birth: 2025-05-21 11:18:37.463682059 +0200

I also tried it on my host, where the filesystem is ZFS using
compression, and there, 'du' will already report a lower value after
creating the image, because of compression. And even without compression
it seems that preallocation=full on ZFS is somehow async :/

> [I] febner@enia ~/qemu/build/tests/qemu-iotests (master)> qemu-img create my.raw 20M -f raw -o preallocation=full
> Formatting 'my.raw', fmt=raw size=20971520 preallocation=full
> [I] febner@enia ~/qemu/build/tests/qemu-iotests (master)> du --block-size=1 my.raw
> 512	my.raw
> [I] febner@enia ~/qemu/build/tests/qemu-iotests (master)> du --block-size=1 my.raw
> 20980224	my.raw

Best Regards,
Fiona