[Qemu-devel] [PATCH 4/5] block: Switch discard length bounds to byte-based

[Eric Blake <eblake@redhat.com>]

Sector-based limits are awkward to think about; in our on-going
quest to move to byte-based interfaces, convert max_discard and
discard_alignment.  Rename them, using 'pdiscard' as an aid to
track which remaining discard interfaces need conversion, and so
that the compiler will help us catch the change in semantics
across any rebased code.  In iscsi.c, sector_limits_lun2qemu()
is no longer needed; and the BlockLimits type is now completely
byte-based.

Signed-off-by: Eric Blake <eblake@redhat.com>
---
 include/block/block_int.h | 21 +++++++++++++++------
 block/io.c                | 16 +++++++++-------
 block/iscsi.c             | 17 ++++++-----------
 block/nbd.c               |  2 +-
 qemu-img.c                |  3 ++-
 5 files changed, 33 insertions(+), 26 deletions(-)

diff --git a/include/block/block_int.h b/include/block/block_int.h
index 96e8476..9dc7af4 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -322,18 +322,27 @@ struct BlockDriver {
 };

 typedef struct BlockLimits {
-    /* maximum number of sectors that can be discarded at once */
-    int max_discard;
+    /* maximum number of bytes that can be discarded at once (since it
+     * is signed, it must be < 2G, if set), should be multiple of
+     * pdiscard_alignment, but need not be power of 2. May be 0 if no
+     * inherent 32-bit limit */
+    int32_t max_pdiscard;

-    /* optimal alignment for discard requests in sectors */
-    int64_t discard_alignment;
+    /* optimal alignment for discard requests in bytes, must be power
+     * of 2, less than max_discard if that is set, and multiple of
+     * bs->request_alignment. May be 0 if bs->request_alignment is
+     * good enough */
+    uint32_t pdiscard_alignment;

     /* maximum number of bytes that can zeroized at once (since it is
-     * signed, it must be < 2G, if set) */
+     * signed, it must be < 2G, if set), should be multiple of
+     * pwrite_zeroes_alignment. May be 0 if no inherent 32-bit limit */
     int32_t max_pwrite_zeroes;

     /* optimal alignment for write zeroes requests in bytes, must be
-     * power of 2, and less than max_pwrite_zeroes if that is set */
+     * power of 2, less than max_pwrite_zeroes if that is set, and
+     * multiple of bs->request_alignment. May be 0 if
+     * bs->request_alignment is good enough */
     uint32_t pwrite_zeroes_alignment;

     /* optimal transfer length in bytes (must be power of 2, and
diff --git a/block/io.c b/block/io.c
index a2bc254..e845ef9 100644
--- a/block/io.c
+++ b/block/io.c
@@ -2255,19 +2255,21 @@ int coroutine_fn bdrv_co_discard(BlockDriverState *bs, int64_t sector_num,
                           BDRV_TRACKED_DISCARD);
     bdrv_set_dirty(bs, sector_num, nb_sectors);

-    max_discard = MIN_NON_ZERO(bs->bl.max_discard, BDRV_REQUEST_MAX_SECTORS);
+    max_discard = MIN_NON_ZERO(bs->bl.max_pdiscard >> BDRV_SECTOR_BITS,
+                               BDRV_REQUEST_MAX_SECTORS);
     while (nb_sectors > 0) {
         int ret;
         int num = nb_sectors;
+        int discard_alignment = bs->bl.pdiscard_alignment >> BDRV_SECTOR_BITS;

         /* align request */
-        if (bs->bl.discard_alignment &&
-            num >= bs->bl.discard_alignment &&
-            sector_num % bs->bl.discard_alignment) {
-            if (num > bs->bl.discard_alignment) {
-                num = bs->bl.discard_alignment;
+        if (discard_alignment &&
+            num >= discard_alignment &&
+            sector_num % discard_alignment) {
+            if (num > discard_alignment) {
+                num = discard_alignment;
             }
-            num -= sector_num % bs->bl.discard_alignment;
+            num -= sector_num % discard_alignment;
         }

         /* limit request size */
diff --git a/block/iscsi.c b/block/iscsi.c
index c5855be..1486443 100644
--- a/block/iscsi.c
+++ b/block/iscsi.c
@@ -1697,11 +1697,6 @@ static void iscsi_close(BlockDriverState *bs)
     memset(iscsilun, 0, sizeof(IscsiLun));
 }

-static int sector_limits_lun2qemu(int64_t sector, IscsiLun *iscsilun)
-{
-    return MIN(sector_lun2qemu(sector, iscsilun), INT_MAX / 2 + 1);
-}
-
 static void iscsi_refresh_limits(BlockDriverState *bs, Error **errp)
 {
     /* We don't actually refresh here, but just return data queried in
@@ -1718,14 +1713,14 @@ static void iscsi_refresh_limits(BlockDriverState *bs, Error **errp)
                               max_xfer_len * iscsilun->block_size);

     if (iscsilun->lbp.lbpu) {
-        if (iscsilun->bl.max_unmap < 0xffffffff) {
-            bs->bl.max_discard =
-                sector_limits_lun2qemu(iscsilun->bl.max_unmap, iscsilun);
+        if (iscsilun->bl.max_unmap < 0xffffffff / iscsilun->block_size) {
+            bs->bl.max_pdiscard =
+                iscsilun->bl.max_unmap * iscsilun->block_size;
         }
-        bs->bl.discard_alignment =
-            sector_limits_lun2qemu(iscsilun->bl.opt_unmap_gran, iscsilun);
+        bs->bl.pdiscard_alignment =
+            iscsilun->bl.opt_unmap_gran * iscsilun->block_size;
     } else {
-        bs->bl.discard_alignment = iscsilun->block_size >> BDRV_SECTOR_BITS;
+        bs->bl.pdiscard_alignment = iscsilun->block_size;
     }

     if (iscsilun->bl.max_ws_len < 0xffffffff / iscsilun->block_size) {
diff --git a/block/nbd.c b/block/nbd.c
index 2ce7b4d..a3de9bc 100644
--- a/block/nbd.c
+++ b/block/nbd.c
@@ -362,7 +362,7 @@ static int nbd_co_flush(BlockDriverState *bs)

 static void nbd_refresh_limits(BlockDriverState *bs, Error **errp)
 {
-    bs->bl.max_discard = UINT32_MAX >> BDRV_SECTOR_BITS;
+    bs->bl.max_pdiscard = INT32_MAX;
     bs->bl.max_transfer = NBD_MAX_BUFFER_SIZE;
 }

diff --git a/qemu-img.c b/qemu-img.c
index 577df0d..26500dc 100644
--- a/qemu-img.c
+++ b/qemu-img.c
@@ -2080,7 +2080,8 @@ static int img_convert(int argc, char **argv)
     bufsectors = MIN(32768,
                      MAX(bufsectors,
                          MAX(out_bs->bl.opt_transfer >> BDRV_SECTOR_BITS,
-                             out_bs->bl.discard_alignment)));
+                             out_bs->bl.pdiscard_alignment >>
+                             BDRV_SECTOR_BITS)));

     if (skip_create) {
         int64_t output_sectors = blk_nb_sectors(out_blk);
-- 
2.5.5