On 11/16/18 9:32 AM, Kevin Wolf wrote:
Am 15.11.2018 um 17:28 hat Eric Blake geschrieben:
On 11/15/18 9:45 AM, Kevin Wolf wrote:
Am 15.11.2018 um 03:03 hat Eric Blake geschrieben:
This change has no semantic impact: all drivers either leave the
value at 0 (no inherent 32-bit limit is still translated into
fragmentation below 2G; see the previous patch for that audit), or
set it to a value less than 2G. However, switching to a larger
type and enforcing the 2G cap at the block layer makes it easier
to audit specific drivers for their robustness to larger sizing,
by letting them specify a value larger than INT_MAX if they have
been audited to be 64-bit clean.
+
+ /* Clamp max_transfer to 2G */
+ if (bs->bl.max_transfer > UINT32_MAX) {
UINT32_MAX is 4G, not 2G.
Would it make more sense to make BDRV_REQUEST_MAX_BYTES the maximum
anyway?
D'oh. Yes, that's what I intended, possibly by spelling it INT_MAX (the
fact that the 'if' goes away in patch 13 is not an excuse for sloppy coding
in the meantime).
INT_MAX is not a different spelling of BDRV_REQUEST_MAX_BYTES. The
latter is slightly lower (0x7ffffe00).
Ah, but:
+ if (bs->bl.max_transfer > UINT32_MAX) {
+ bs->bl.max_transfer = QEMU_ALIGN_DOWN(BDRV_REQUEST_MAX_BYTES,
+ MAX(bs->bl.opt_transfer,
+ bs->bl.request_alignment));
+ }
QEMU_ALIGN_DOWN() will change INT_MAX to BDRV_REQUEST_MAX_BYTES if
bs->bl.request_alignment is 512 and opt_transfer is 0; and if either
alignment number is larger than 512, max_transfer is capped even lower
regardless of whether I was aligning INT_MAX or BDRV_REQUEST_MAX_BYTES
down to an alignment boundary.
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3266
Virtualization: qemu.org | libvirt.org
