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block: Make supported_write_flags a per-bds property

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Pre-patch, .supported_write_flags lives at the driver level, which
means we are blindly declaring that all block devices using a
given driver will either equally support FUA, or that we need a
fallback at the block layer.  But there are drivers where FUA
support is a per-block decision: the NBD block driver is dependent
on the remote server advertising NBD_FLAG_SEND_FUA (and has
fallback code to duplicate the flush that the block layer would do
if NBD had not set .supported_write_flags); and the iscsi block
driver is dependent on the mode sense bits advertised by the
underlying device (and is currently silently ignoring FUA requests
if the underlying device does not support FUA).

The fix is to make supported flags as a per-BDS option, set during
.bdrv_open().  This patch moves the variable and fixes NBD and iscsi
to set it only conditionally; later patches will then further
simplify the NBD driver to quit duplicating work done at the block
layer, as well as tackle the fact that SCSI does not support FUA
semantics on WRITESAME(10/16) but only on WRITE(10/16).

Signed-off-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Fam Zheng <famz@redhat.com>
Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Eric Blake 2016-05-03 16:39:06 -06:00 • committed by Kevin Wolf
parent 2928abce6d
commit 4df863f336
6 changed files with 17 additions and 14 deletions
Download patch file Download diff file Expand all files Collapse all files

10
block/iscsi.c
View file

@ -456,8 +456,11 @@ iscsi_co_writev_flags(BlockDriverState *bs, int64_t sector_num, int nb_sectors,
struct IscsiTask iTask;
uint64_t lba;
uint32_t num_sectors;
bool fua;
bool fua = flags & BDRV_REQ_FUA;
if (fua) {
assert(iscsilun->dpofua);
}
if (!is_request_lun_aligned(sector_num, nb_sectors, iscsilun)) {
return -EINVAL;
}
@ -472,7 +475,6 @@ iscsi_co_writev_flags(BlockDriverState *bs, int64_t sector_num, int nb_sectors,
num_sectors = sector_qemu2lun(nb_sectors, iscsilun);
iscsi_co_init_iscsitask(iscsilun, &iTask);
retry:
fua = iscsilun->dpofua && (flags & BDRV_REQ_FUA);
if (iscsilun->use_16_for_rw) {
iTask.task = iscsi_write16_task(iscsilun->iscsi, iscsilun->lun, lba,
NULL, num_sectors * iscsilun->block_size,
@ -1548,6 +1550,9 @@ static int iscsi_open(BlockDriverState *bs, QDict *options, int flags,
task = NULL;
iscsi_modesense_sync(iscsilun);
if (iscsilun->dpofua) {
bs->supported_write_flags = BDRV_REQ_FUA;
}
/* Check the write protect flag of the LUN if we want to write */
if (iscsilun->type == TYPE_DISK && (flags & BDRV_O_RDWR) &&
@ -1841,7 +1846,6 @@ static BlockDriver bdrv_iscsi = {
.bdrv_co_write_zeroes = iscsi_co_write_zeroes,
.bdrv_co_readv = iscsi_co_readv,
.bdrv_co_writev_flags = iscsi_co_writev_flags,
.supported_write_flags = BDRV_REQ_FUA,
.bdrv_co_flush_to_disk = iscsi_co_flush,
#ifdef __linux__