block: add discard support

Add a new bdrv_discard method to free blocks in a mapping image, and a new
drive property to set the granularity for these discard.  If no discard
granularity support is set discard support is disabled.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

block.c

@@ -1515,6 +1515,17 @@ int bdrv_has_zero_init(BlockDriverState *bs)
     return 1;
 }
 
+int bdrv_discard(BlockDriverState *bs, int64_t sector_num, int nb_sectors)
+{
+    if (!bs->drv) {
+        return -ENOMEDIUM;
+    }
+    if (!bs->drv->bdrv_discard) {
+        return 0;
+    }
+    return bs->drv->bdrv_discard(bs, sector_num, nb_sectors);
+}
+
 /*
  * Returns true iff the specified sector is present in the disk image. Drivers
  * not implementing the functionality are assumed to not support backing files,

block.h

@@ -146,6 +146,7 @@ int bdrv_flush(BlockDriverState *bs);
 void bdrv_flush_all(void);
 void bdrv_close_all(void);
 
+int bdrv_discard(BlockDriverState *bs, int64_t sector_num, int nb_sectors);
 int bdrv_has_zero_init(BlockDriverState *bs);
 int bdrv_is_allocated(BlockDriverState *bs, int64_t sector_num, int nb_sectors,
 	int *pnum);

block/raw.c

@@ -65,6 +65,11 @@ static int raw_probe(const uint8_t *buf, int buf_size, const char *filename)
    return 1; /* everything can be opened as raw image */
 }
 
+static int raw_discard(BlockDriverState *bs, int64_t sector_num, int nb_sectors)
+{
+    return bdrv_discard(bs->file, sector_num, nb_sectors);
+}
+
 static int raw_is_inserted(BlockDriverState *bs)
 {
     return bdrv_is_inserted(bs->file);
@@ -130,6 +135,7 @@ static BlockDriver bdrv_raw = {
     .bdrv_aio_readv     = raw_aio_readv,
     .bdrv_aio_writev    = raw_aio_writev,
     .bdrv_aio_flush     = raw_aio_flush,
+    .bdrv_discard       = raw_discard,
 
     .bdrv_is_inserted   = raw_is_inserted,
     .bdrv_eject         = raw_eject,

block_int.h

@@ -72,6 +72,8 @@ struct BlockDriver {
         BlockDriverCompletionFunc *cb, void *opaque);
     BlockDriverAIOCB *(*bdrv_aio_flush)(BlockDriverState *bs,
         BlockDriverCompletionFunc *cb, void *opaque);
+    int (*bdrv_discard)(BlockDriverState *bs, int64_t sector_num,
+                        int nb_sectors);
 
     int (*bdrv_aio_multiwrite)(BlockDriverState *bs, BlockRequest *reqs,
         int num_reqs);
@@ -227,6 +229,7 @@ typedef struct BlockConf {
     uint16_t min_io_size;
     uint32_t opt_io_size;
     int32_t bootindex;
+    uint32_t discard_granularity;
 } BlockConf;
 
 static inline unsigned int get_physical_block_exp(BlockConf *conf)
@@ -250,6 +253,8 @@ static inline unsigned int get_physical_block_exp(BlockConf *conf)
                        _conf.physical_block_size, 512),                 \
     DEFINE_PROP_UINT16("min_io_size", _state, _conf.min_io_size, 0),  \
     DEFINE_PROP_UINT32("opt_io_size", _state, _conf.opt_io_size, 0),    \
-    DEFINE_PROP_INT32("bootindex", _state, _conf.bootindex, -1)         \
+    DEFINE_PROP_INT32("bootindex", _state, _conf.bootindex, -1),        \
+    DEFINE_PROP_UINT32("discard_granularity", _state, \
+                       _conf.discard_granularity, 0)
 
 #endif /* BLOCK_INT_H */