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scsi: reference-count requests

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With the next patch, a device may hold SCSIRequest for an indefinite
time.  Split a rather big patch, and protect against access errors,
by reference counting them.

There is some ugliness in scsi_send_command implementation due to
the need to unref the request when it fails.  This will go away
with the next patches, which move the unref'ing to the devices.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
This commit is contained in:
Paolo Bonzini 2011-04-18 16:01:56 +02:00
parent d33e0ce213
commit ad2d30f79d
4 changed files with 58 additions and 23 deletions
Download patch file Download diff file Expand all files Collapse all files

29
hw/scsi-bus.c
View file

@ -136,6 +136,8 @@ SCSIRequest *scsi_req_alloc(size_t size, SCSIDevice *d, uint32_t tag, uint32_t l
SCSIRequest *req;
req = qemu_mallocz(size);
/* Two references: one is passed back to the HBA, one is in d->requests. */
req->refcount = 2;
req->bus = scsi_bus_from_device(d);
req->dev = d;
req->tag = tag;
@ -159,21 +161,16 @@ SCSIRequest *scsi_req_find(SCSIDevice *d, uint32_t tag)
return NULL;
}
static void scsi_req_dequeue(SCSIRequest *req)
void scsi_req_dequeue(SCSIRequest *req)
{
trace_scsi_req_dequeue(req->dev->id, req->lun, req->tag);
if (req->enqueued) {
QTAILQ_REMOVE(&req->dev->requests, req, next);
req->enqueued = false;
scsi_req_unref(req);
}
}
void scsi_req_free(SCSIRequest *req)
{
scsi_req_dequeue(req);
qemu_free(req);
}
static int scsi_req_length(SCSIRequest *req, uint8_t *cmd)
{
switch (cmd[0] >> 5) {
@ -495,6 +492,22 @@ static const char *scsi_command_name(uint8_t cmd)
return names[cmd];
}
SCSIRequest *scsi_req_ref(SCSIRequest *req)
{
req->refcount++;
return req;
}
void scsi_req_unref(SCSIRequest *req)
{
if (--req->refcount == 0) {
if (req->dev->info->free_req) {
req->dev->info->free_req(req);
}
qemu_free(req);
}
}
/* Called by the devices when data is ready for the HBA. The HBA should
start a DMA operation to read or fill the device's data buffer.
Once it completes, calling one of req->dev->info->read_data or
@ -537,10 +550,12 @@ void scsi_req_print(SCSIRequest *req)
void scsi_req_complete(SCSIRequest *req)
{
assert(req->status != -1);
scsi_req_ref(req);
scsi_req_dequeue(req);
req->bus->ops->complete(req->bus, SCSI_REASON_DONE,
req->tag,
req->status);
scsi_req_unref(req);
}
static char *scsibus_get_fw_dev_path(DeviceState *dev)