[Qemu-devel] [PATCH v2 3/5] block: Allow NULL file for bdrv_get_block_status()

[Eric Blake <eblake@redhat.com>]

Not all callers care about which BDS owns the mapping for a given
range of the file.  This patch merely simplifies the callers by
consolidating the logic in the common call point, while guaranteeing
a non-NULL file to all the driver callbacks, for no semantic change.

However, this will also set the stage for a future cleanup: when a
caller does not care about which BDS owns an offset, it would be
nice to allow the driver to optimize things to not have to return
BDRV_BLOCK_OFFSET_VALID in the first place.  In the case of fragmented
allocation (for example, it's fairly easy to create a qcow2 image
where consecutive guest addresses are not at consecutive host
addresses), the current contract requires bdrv_get_block_status()
to clamp *pnum to the limit where host addresses are no longer
consecutive, but allowing a NULL file means that *pnum could be
set to the full length of known-allocated data.

Signed-off-by: Eric Blake <eblake@redhat.com>

---
v2: new patch
---
 block/io.c     | 15 +++++++++------
 block/mirror.c |  3 +--
 block/qcow2.c  |  4 +---
 qemu-img.c     | 10 ++++------
 4 files changed, 15 insertions(+), 17 deletions(-)

diff --git a/block/io.c b/block/io.c
index 8e6c3fe..eea74cb 100644
--- a/block/io.c
+++ b/block/io.c
@@ -706,7 +706,6 @@ int bdrv_make_zero(BdrvChild *child, BdrvRequestFlags flags)
 {
     int64_t target_sectors, ret, nb_sectors, sector_num = 0;
     BlockDriverState *bs = child->bs;
-    BlockDriverState *file;
     int n;

     target_sectors = bdrv_nb_sectors(bs);
@@ -719,7 +718,7 @@ int bdrv_make_zero(BdrvChild *child, BdrvRequestFlags flags)
         if (nb_sectors <= 0) {
             return 0;
         }
-        ret = bdrv_get_block_status(bs, sector_num, nb_sectors, &n, &file);
+        ret = bdrv_get_block_status(bs, sector_num, nb_sectors, &n, NULL);
         if (ret < 0) {
             error_report("error getting block status at sector %" PRId64 ": %s",
                          sector_num, strerror(-ret));
@@ -1737,8 +1736,9 @@ typedef struct BdrvCoGetBlockStatusData {
  * 'nb_sectors' is the max value 'pnum' should be set to.  If nb_sectors goes
  * beyond the end of the disk image it will be clamped.
  *
- * If returned value is positive and BDRV_BLOCK_OFFSET_VALID bit is set, 'file'
- * points to the BDS which the sector range is allocated in.
+ * If returned value is positive, BDRV_BLOCK_OFFSET_VALID bit is set, and
+ * 'file' is non-NULL, then '*file' points to the BDS which the sector range
+ * is allocated in.
  */
 static int64_t coroutine_fn bdrv_co_get_block_status(BlockDriverState *bs,
                                                      int64_t sector_num,
@@ -1748,7 +1748,11 @@ static int64_t coroutine_fn bdrv_co_get_block_status(BlockDriverState *bs,
     int64_t total_sectors;
     int64_t n;
     int64_t ret, ret2;
+    BlockDriverState *tmpfile;

+    if (!file) {
+        file = &tmpfile;
+    }
     *file = NULL;
     total_sectors = bdrv_nb_sectors(bs);
     if (total_sectors < 0) {
@@ -1916,9 +1920,8 @@ int64_t bdrv_get_block_status(BlockDriverState *bs,
 int coroutine_fn bdrv_is_allocated(BlockDriverState *bs, int64_t sector_num,
                                    int nb_sectors, int *pnum)
 {
-    BlockDriverState *file;
     int64_t ret = bdrv_get_block_status(bs, sector_num, nb_sectors, pnum,
-                                        &file);
+                                        NULL);
     if (ret < 0) {
         return ret;
     }
diff --git a/block/mirror.c b/block/mirror.c
index e86f8f8..4563ba7 100644
--- a/block/mirror.c
+++ b/block/mirror.c
@@ -392,7 +392,6 @@ static uint64_t coroutine_fn mirror_iteration(MirrorBlockJob *s)
     while (nb_chunks > 0 && sector_num < end) {
         int64_t ret;
         int io_sectors, io_sectors_acct;
-        BlockDriverState *file;
         enum MirrorMethod {
             MIRROR_METHOD_COPY,
             MIRROR_METHOD_ZERO,
@@ -402,7 +401,7 @@ static uint64_t coroutine_fn mirror_iteration(MirrorBlockJob *s)
         assert(!(sector_num % sectors_per_chunk));
         ret = bdrv_get_block_status_above(source, NULL, sector_num,
                                           nb_chunks * sectors_per_chunk,
-                                          &io_sectors, &file);
+                                          &io_sectors, NULL);
         if (ret < 0) {
             io_sectors = MIN(nb_chunks * sectors_per_chunk, max_io_sectors);
         } else if (ret & BDRV_BLOCK_DATA) {
diff --git a/block/qcow2.c b/block/qcow2.c
index b3ba5da..8e9e29b 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -2448,7 +2448,6 @@ static bool is_zero_sectors(BlockDriverState *bs, int64_t start,
                             uint32_t count)
 {
     int nr;
-    BlockDriverState *file;
     int64_t res;

     if (start + count > bs->total_sectors) {
@@ -2458,8 +2457,7 @@ static bool is_zero_sectors(BlockDriverState *bs, int64_t start,
     if (!count) {
         return true;
     }
-    res = bdrv_get_block_status_above(bs, NULL, start, count,
-                                      &nr, &file);
+    res = bdrv_get_block_status_above(bs, NULL, start, count, &nr, NULL);
     return res >= 0 && (res & BDRV_BLOCK_ZERO) && nr == count;
 }

diff --git a/qemu-img.c b/qemu-img.c
index 5aef8ef..cb78696 100644
--- a/qemu-img.c
+++ b/qemu-img.c
@@ -1398,7 +1398,6 @@ static int img_compare(int argc, char **argv)

     for (;;) {
         int64_t status1, status2;
-        BlockDriverState *file;

         nb_sectors = sectors_to_process(total_sectors, sector_num);
         if (nb_sectors <= 0) {
@@ -1406,7 +1405,7 @@ static int img_compare(int argc, char **argv)
         }
         status1 = bdrv_get_block_status_above(bs1, NULL, sector_num,
                                               total_sectors1 - sector_num,
-                                              &pnum1, &file);
+                                              &pnum1, NULL);
         if (status1 < 0) {
             ret = 3;
             error_report("Sector allocation test failed for %s", filename1);
@@ -1416,7 +1415,7 @@ static int img_compare(int argc, char **argv)

         status2 = bdrv_get_block_status_above(bs2, NULL, sector_num,
                                               total_sectors2 - sector_num,
-                                              &pnum2, &file);
+                                              &pnum2, NULL);
         if (status2 < 0) {
             ret = 3;
             error_report("Sector allocation test failed for %s", filename2);
@@ -1615,15 +1614,14 @@ static int convert_iteration_sectors(ImgConvertState *s, int64_t sector_num)
     n = MIN(s->total_sectors - sector_num, BDRV_REQUEST_MAX_SECTORS);

     if (s->sector_next_status <= sector_num) {
-        BlockDriverState *file;
         if (s->target_has_backing) {
             ret = bdrv_get_block_status(blk_bs(s->src[src_cur]),
                                         sector_num - src_cur_offset,
-                                        n, &n, &file);
+                                        n, &n, NULL);
         } else {
             ret = bdrv_get_block_status_above(blk_bs(s->src[src_cur]), NULL,
                                               sector_num - src_cur_offset,
-                                              n, &n, &file);
+                                              n, &n, NULL);
         }
         if (ret < 0) {
             return ret;
-- 
2.9.4