Improve errors when transfering image for conversion

[MusicDin]

Please confirm

• [x] I have searched existing issues to check if an issue already exists for the bug I encountered.

Distribution

Ubuntu

Distribution version

24

Output of "snap list --all lxd core20 core22 core24 snapd"

LXD 5.21/6.X

Output of "lxc info" or system info if it fails

LXD 5.21/6.X

Issue description

When uploading a non-raw image to the server for conversion, the initial transfer to backups directory can fail if there is no sufficient size. The server errors out with No space left. This can be misleading as the error does not indicate that there is not enough space in the backups directory.

Additionally, we should hint the server with the initial image size and verify that backups directory/volume can accommodate the image before the transfer.

Steps to reproduce

Use lxd-migrate with backups volume that does not have enough space to accommodate the uploaded (compressed) image.

Information to attach

• [ ] Any relevant kernel output (dmesg)
• [ ] Instance log (lxc info NAME --show-log)
• [ ] Instance configuration (lxc config show NAME --expanded)
• [ ] Main daemon log (at /var/log/lxd/lxd.log or /var/snap/lxd/common/lxd/logs/lxd.log)
• [ ] Output of the client with --debug
• [ ] Output of the daemon with --debug (or use lxc monitor while reproducing the issue)

[tomponline]

@MusicDin is this the same as https://github.com/canonical/lxd/issues/14256 ?