[Qemu-devel] [PATCH] scsi-disk: add non-zero MAX UNMAP LBA COUNT to block limits VPD page

[Qemu-devel] [PATCH] scsi-disk: add non-zero MAX UNMAP LBA COUNT to block limits VPD page

[Paolo Bonzini]

Linux prefers WRITE SAME to UNMAP if the count is zero, and WRITE
SAME does not discard anything unless the device can guarantee that
the resulting block is zero.

This fixes thin provisioning on glusterfs.

Reported-by: Bharata B Rao <bharata@linux.vnet.ibm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 hw/scsi/scsi-disk.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/hw/scsi/scsi-disk.c b/hw/scsi/scsi-disk.c
index 7653411..156c965 100644
--- a/hw/scsi/scsi-disk.c
+++ b/hw/scsi/scsi-disk.c
@@ -74,6 +74,7 @@ struct SCSIDiskState
     bool media_event;
     bool eject_request;
     uint64_t wwn;
+    uint64_t max_unmap_size;
     QEMUBH *bh;
     char *version;
     char *serial;
@@ -625,6 +626,8 @@ static int scsi_disk_emulate_inquiry(SCSIRequest *req, uint8_t *outbuf)
                     s->qdev.conf.min_io_size / s->qdev.blocksize;
             unsigned int opt_io_size =
                     s->qdev.conf.opt_io_size / s->qdev.blocksize;
+	    unsigned int max_unmap_sectors =
+		    s->max_unmap_size / s->qdev.blocksize; /* 1 GB */
 
             if (s->qdev.type == TYPE_ROM) {
                 DPRINTF("Inquiry (EVPD[%02X] not supported for CDROM\n",
@@ -647,6 +650,12 @@ static int scsi_disk_emulate_inquiry(SCSIRequest *req, uint8_t *outbuf)
             outbuf[14] = (opt_io_size >> 8) & 0xff;
             outbuf[15] = opt_io_size & 0xff;
 
+            /* maximum unmap LBA count, hardcoded to 1GB */
+            outbuf[20] = (max_unmap_sectors >> 24) & 0xff;
+            outbuf[21] = (max_unmap_sectors >> 16) & 0xff;
+            outbuf[22] = (max_unmap_sectors >> 8) & 0xff;
+            outbuf[23] = max_unmap_sectors & 0xff;
+
             /* optimal unmap granularity */
             outbuf[28] = (unmap_sectors >> 24) & 0xff;
             outbuf[29] = (unmap_sectors >> 16) & 0xff;
@@ -2519,6 +2528,7 @@ static Property scsi_hd_properties[] = {
     DEFINE_PROP_BIT("dpofua", SCSIDiskState, features,
                     SCSI_DISK_F_DPOFUA, false),
     DEFINE_PROP_HEX64("wwn", SCSIDiskState, wwn, 0),
+    DEFINE_PROP_UINT64("max_unmap_size", SCSIDiskState, max_unmap_size, 1 << 30),
     DEFINE_BLOCK_CHS_PROPERTIES(SCSIDiskState, qdev.conf),
     DEFINE_PROP_END_OF_LIST(),
 };
@@ -2628,6 +2638,7 @@ static Property scsi_disk_properties[] = {
     DEFINE_PROP_BIT("dpofua", SCSIDiskState, features,
                     SCSI_DISK_F_DPOFUA, false),
     DEFINE_PROP_HEX64("wwn", SCSIDiskState, wwn, 0),
+    DEFINE_PROP_UINT64("max_unmap_size", SCSIDiskState, max_unmap_size, 1 << 30),
     DEFINE_PROP_END_OF_LIST(),
 };
 
-- 
1.8.4.2

Re: [Qemu-devel] [PATCH] scsi-disk: add non-zero MAX UNMAP LBA COUNT to block limits VPD page

[Bharata B Rao]

On Fri, Dec 20, 2013 at 03:58:08PM +0100, Paolo Bonzini wrote:
> Linux prefers WRITE SAME to UNMAP if the count is zero, and WRITE
> SAME does not discard anything unless the device can guarantee that
> the resulting block is zero.
> 
> This fixes thin provisioning on glusterfs.

I don't see discard requests reaching GlusterFS even after this patch.
bdrv_co_discard or bdrv_aio_discard isn't getting called for the gluster
drive.

Regards,
Bharata.