CVS commit: src/sys/arch/xen/xen

["Manuel Bouyer" <bouyer%netbsd.org@localhost>]

Module Name:    src
Committed By:   bouyer
Date:           Wed Jun 19 09:02:49 UTC 2024

Modified Files:
        src/sys/arch/xen/xen: xbdback_xenbus.c

Log Message:
Restore "sparse" segements support which was lost in rev 1.83, causing
VBD corruption with linux guests.
The segments in a single request are not always contigous in VA; this means
that the end of a segment is not always 7 and the start of the next one is not
always 0. When this happens this means that a contigous chunk of data from
disk has to be dispatched to various non-contigous VA, in chunks of VBD_BSIZE
bytes (or the other way round for writes).
Linux I/O subsystems seems to support this natively; to emulate this allocate
a MAXPHYS bounce buffer to do the I/O and then memcpy() the data from/to
the segments as requested. If the request is contigous do the I/O
directly to the mapped VA.

This means that we need to keep segments details until iodone(); so move
the blkif_request_segment array from xbdback_instance to xbdback_io. The
array is allocated separately to guarantee proper page alignement.

non-contigous segments seems rare so allocate one bounce buffer per
xbdback_instance, and stall the ring if the bounce buffer is already in use.
For this add back a mechanism to restart an I/O at a specific point
after thread sleep/wakeup.

While there guard some more printfs with ratecheck() and add more checks on
segments bounds.

Tested with a HVM scientific linux install from iso image; the install would
fail with a xfs corruption when installing grub.


To generate a diff of this commit:
cvs rdiff -u -r1.104 -r1.105 src/sys/arch/xen/xen/xbdback_xenbus.c

Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.