Previously this message goes to /dev/null (unless BACKUP_DEBUG enabled),
so the user got cryptic "Restore failed" message without any clue about
the cause.
When non-english language is set, some processes can output non-ASCII
characters in error messages. Handle them nicely.
Also make error messages more consistent about "ERROR:" prefix. Do not
use this prefix in QubesException message, add it just before showing
the message to the user.
The --xform option affects all the names - including symlink targets. So
make the pattern as precise as possible to not break symlinks in dom0
home backup. Still not ideal, but at least limit damage to relative
symlinks pointing at <username> directory (which hopefully user will
not create). Previous version broke all relative symlinks...
Apparently kernel patch "x86/cpa: Use pte_attrs instead of pte_flags on
CPA/set_p.._wb/wc operations" (in out repo) doesn't fully solve the
problem and sometimes qubes-gui agent crashes with message like
"qubes-gui:664 map pfn expected mapping type write-back for [mem
0x00093000-0x00093fff], got uncached-minus".
Because PAT we really need only in dom0 (lack of it dramatically
decrease performance of some graphics drivers), we can simply disable it
in VM - as it is currently done in upstream kernel.
The backup_cancel() method kills processes registered by main thread and
set "running_backup_operation.canceled" to True. Then main thread get an
error because of killed processes and check if that was because of
cancel request.
Introduce BackupCanceledError, which can report temporary dir to remove.
Do wait for nest reported filename only when restoring directly from
dom0. In VM case it isn't necessary and will cause false error report
(because filename will be set to nextfile at the end of restore process,
so will be treated as spurious file without hmac).
Simply get device major-minor from /dev/ device file.
This is only partial solution, because this will work only for dom0
devices, but the same problem can apply to VM.
It stores basic backup information like used hmac/crypto algorithm,
whether backup is encrypted/compressed and possibly more. The header
file is parsed only after successful HMAC verification. Because we do
not know which HMAC algorithm was used before reading the header, try to
guess trying all supported (starting with the default one).
Backup header is stored as the first file, which is always not encrypted
and not compressed. Then qubes.xml follows.
