Am 21.06.2013 um 11:45 hat Peter Lieven geschrieben:
> Am 21.06.2013 11:18, schrieb Kevin Wolf:
> > Am 20.06.2013 um 20:20 hat Peter Lieven geschrieben:
> >> Signed-off-by: Peter Lieven <p...@kamp.de>
> >> ---
> >> block/iscsi.c | 57
> >> +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> >> 1 file changed, 57 insertions(+)
> >>
> >> diff --git a/block/iscsi.c b/block/iscsi.c
> >> index 0bbf0b1..e6b966d 100644
> >> --- a/block/iscsi.c
> >> +++ b/block/iscsi.c
> >> @@ -49,6 +49,7 @@ typedef struct IscsiLun {
> >> uint64_t num_blocks;
> >> int events;
> >> QEMUTimer *nop_timer;
> >> + uint8_t lbpme;
> >> } IscsiLun;
> >>
> >> typedef struct IscsiAIOCB {
> >> @@ -800,6 +801,60 @@ iscsi_getlength(BlockDriverState *bs)
> >> return len;
> >> }
> >>
> >> +static int coroutine_fn iscsi_co_is_allocated(BlockDriverState *bs,
> >> + int64_t sector_num,
> >> + int nb_sectors, int *pnum)
> >> +{
> >> + IscsiLun *iscsilun = bs->opaque;
> >> + struct scsi_task *task = NULL;
> >> + struct scsi_get_lba_status *lbas = NULL;
> >> + struct scsi_lba_status_descriptor *lbasd = NULL;
> >> + int ret;
> >> +
> >> + *pnum = nb_sectors;
> >> +
> >> + if (iscsilun->lbpme == 0) {
> >> + return 1;
> >> + }
> >> +
> >> + /* in-flight requests could invalidate the lba status result */
> >> + while (iscsi_process_flush(iscsilun)) {
> >> + qemu_aio_wait();
> >> + }
> > Note that you're blocking here. The preferred way would be something
> > involving a yield from the coroutine and a reenter as soon as all
> > requests are done. Maybe a CoRwLock does what you need?
> Is there a document how to use it? Or can you help here?
The idea would be to take a read lock while any request is in flight
(i.e. qemu_co_rwlock_rdlock() before it's started and
qemu_co_rwlock_unlock() when it completes), and to take a write lock
(qemu_co_rwlock_wrlock) for the part of iscsi_co_is_allocated() that
requires that no other request runs in parallel.
> >> + if (task == NULL || task->status != SCSI_STATUS_GOOD) {
> >> + scsi_free_scsi_task(task);
> >> + return 1;
> > Error cases should set *pnum = 0 and return 0.
> In this special case, the target might not implement get_lba_status
> or it might return SCSI_STATUS_BUSY. We shouldn't generate an
> error or should we?
If you have reasons to not return an error, do so. Maybe adding a
comment wouldn't hurt.
I just saw more than one of these return 1; lines which looked like
error handling to me. If you don't want any of them to result in an
error, that's okay with me, I just wanted to mention how you would
correctly signal an error.
Kevin
