[Qemu-devel] [PATCH 09/10] scsi-disk: lazily allocate bounce buffer

[Paolo Bonzini <pbonzini@redhat.com>]

It will not be needed for reads and writes if the HBA provides a sglist.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 hw/scsi-disk.c |   33 ++++++++++++++++++++++-----------
 1 files changed, 22 insertions(+), 11 deletions(-)

diff --git a/hw/scsi-disk.c b/hw/scsi-disk.c
index 37dd9d6..509407f 100644
--- a/hw/scsi-disk.c
+++ b/hw/scsi-disk.c
@@ -54,6 +54,7 @@ typedef struct SCSIDiskReq {
     /* Both sector and sector_count are in terms of qemu 512 byte blocks.  */
     uint64_t sector;
     uint32_t sector_count;
+    uint32_t buflen;
     struct iovec iov;
     QEMUIOVector qiov;
     uint32_t status;
@@ -77,13 +78,15 @@ struct SCSIDiskState
 };
 
 static int scsi_handle_rw_error(SCSIDiskReq *r, int error, int type);
-static int scsi_disk_emulate_command(SCSIDiskReq *r, uint8_t *outbuf);
+static int scsi_disk_emulate_command(SCSIDiskReq *r);
 
 static void scsi_free_request(SCSIRequest *req)
 {
     SCSIDiskReq *r = DO_UPCAST(SCSIDiskReq, req, req);
 
-    qemu_vfree(r->iov.iov_base);
+    if (r->iov.iov_base) {
+        qemu_vfree(r->iov.iov_base);
+    }
 }
 
 /* Helper function for command completion with sense.  */
@@ -109,7 +112,13 @@ static void scsi_cancel_io(SCSIRequest *req)
 
 static uint32_t scsi_init_iovec(SCSIDiskReq *r)
 {
-    r->iov.iov_len = MIN(r->sector_count * 512, SCSI_DMA_BUF_SIZE);
+    SCSIDiskState *s = DO_UPCAST(SCSIDiskState, qdev, r->req.dev);
+
+    if (!r->iov.iov_base) {
+        r->buflen = SCSI_DMA_BUF_SIZE;
+        r->iov.iov_base = qemu_blockalign(s->bs, r->buflen);
+    }
+    r->iov.iov_len = MIN(r->sector_count * 512, r->buflen);
     qemu_iovec_init_external(&r->qiov, &r->iov, 1);
     return r->qiov.size / 512;
 }
@@ -288,7 +297,7 @@ static void scsi_dma_restart_bh(void *opaque)
                 scsi_write_data(&r->req);
                 break;
             case SCSI_REQ_STATUS_RETRY_FLUSH:
-                ret = scsi_disk_emulate_command(r, r->iov.iov_base);
+                ret = scsi_disk_emulate_command(r);
                 if (ret == 0) {
                     scsi_req_complete(&r->req, GOOD);
                 }
@@ -780,14 +789,21 @@ static int scsi_disk_emulate_read_toc(SCSIRequest *req, uint8_t *outbuf)
     return toclen;
 }
 
-static int scsi_disk_emulate_command(SCSIDiskReq *r, uint8_t *outbuf)
+static int scsi_disk_emulate_command(SCSIDiskReq *r)
 {
     SCSIRequest *req = &r->req;
     SCSIDiskState *s = DO_UPCAST(SCSIDiskState, qdev, req->dev);
     uint64_t nb_sectors;
+    uint8_t *outbuf;
     int buflen = 0;
     int ret;
 
+    if (!r->iov.iov_base) {
+        r->buflen = 4096;
+        r->iov.iov_base = qemu_blockalign(s->bs, 4096);
+    }
+
+    outbuf = r->iov.iov_base;
     switch (req->cmd.buf[0]) {
     case TEST_UNIT_READY:
         if (!bdrv_is_inserted(s->bs))
@@ -950,11 +966,9 @@ static int32_t scsi_send_command(SCSIRequest *req, uint8_t *buf)
     SCSIDiskState *s = DO_UPCAST(SCSIDiskState, qdev, req->dev);
     int32_t len;
     uint8_t command;
-    uint8_t *outbuf;
     int rc;
 
     command = buf[0];
-    outbuf = (uint8_t *)r->iov.iov_base;
     DPRINTF("Command: lun=%d tag=0x%x data=0x%02x", req->lun, req->tag, buf[0]);
 
 #ifdef DEBUG_SCSI
@@ -985,7 +999,7 @@ static int32_t scsi_send_command(SCSIRequest *req, uint8_t *buf)
     case SERVICE_ACTION_IN:
     case VERIFY:
     case REZERO_UNIT:
-        rc = scsi_disk_emulate_command(r, outbuf);
+        rc = scsi_disk_emulate_command(r);
         if (rc < 0) {
             return 0;
         }
@@ -1206,11 +1220,8 @@ static SCSIRequest *scsi_new_request(SCSIDevice *d, uint32_t tag,
 {
     SCSIDiskState *s = DO_UPCAST(SCSIDiskState, qdev, d);
     SCSIRequest *req;
-    SCSIDiskReq *r;
 
     req = scsi_req_alloc(&scsi_disk_reqops, &s->qdev, tag, lun, hba_private);
-    r = DO_UPCAST(SCSIDiskReq, req, req);
-    r->iov.iov_base = qemu_blockalign(s->bs, SCSI_DMA_BUF_SIZE);
     return req;
 }
 
-- 
1.7.6