[Qemu-devel] [PATCH 3/3] dmg: use qemu block API

[Christoph Hellwig]

Use bdrv_pwrite to access the backing device instead of pread, and
convert the driver to implementing the bdrv_open method which gives
it an already opened BlockDriverState for the underlying device.

Dmg actually does an lseek to a negative offset in the open routine,
which we replace with offset arithmetics after doing a bdrv_getlength.

Signed-off-by: Christoph Hellwig <address@hidden>


Index: qemu-kevin/block/dmg.c
===================================================================
--- qemu-kevin.orig/block/dmg.c 2010-05-07 16:44:10.487253603 +0200
+++ qemu-kevin/block/dmg.c      2010-05-07 16:44:10.829253954 +0200
@@ -28,8 +28,6 @@
 #include <zlib.h>
 
 typedef struct BDRVDMGState {
-    int fd;
-
     /* each chunk contains a certain number of sectors,
      * offsets[i] is the offset in the .dmg file,
      * lengths[i] is the length of the compressed chunk,
@@ -58,23 +56,23 @@ static int dmg_probe(const uint8_t *buf,
     return 0;
 }
 
-static off_t read_off(int fd, int64_t offset)
+static off_t read_off(BlockDriverState *bs, int64_t offset)
 {
        uint64_t buffer;
-       if (pread(fd, &buffer, 8, offset) < 8)
+       if (bdrv_pread(bs->file, offset, &buffer, 8) < 8)
                return 0;
        return be64_to_cpu(buffer);
 }
 
-static off_t read_uint32(int fd, int64_t offset)
+static off_t read_uint32(BlockDriverState *bs, int64_t offset)
 {
        uint32_t buffer;
-       if (pread(fd, &buffer, 4, offset) < 4)
+       if (bdrv_pread(bs->file, offset, &buffer, 4) < 4)
                return 0;
        return be32_to_cpu(buffer);
 }
 
-static int dmg_open(BlockDriverState *bs, const char *filename, int flags)
+static int dmg_open(BlockDriverState *bs, int flags)
 {
     BDRVDMGState *s = bs->opaque;
     off_t info_begin,info_end,last_in_offset,last_out_offset;
@@ -82,29 +80,27 @@ static int dmg_open(BlockDriverState *bs
     uint32_t max_compressed_size=1,max_sectors_per_chunk=1,i;
     int64_t offset;
 
-    s->fd = open(filename, O_RDONLY | O_BINARY);
-    if (s->fd < 0)
-        return -errno;
     bs->read_only = 1;
     s->n_chunks = 0;
     s->offsets = s->lengths = s->sectors = s->sectorcounts = NULL;
 
     /* read offset of info blocks */
-    offset = lseek(s->fd, -0x1d8, SEEK_END);
+    offset = bdrv_getlength(bs->file);
     if (offset < 0) {
         goto fail;
     }
+    offset -= 0x1d8;
 
-    info_begin = read_off(s->fd, offset);
+    info_begin = read_off(bs, offset);
     if (info_begin == 0) {
        goto fail;
     }
 
-    if (read_uint32(s->fd, info_begin) != 0x100) {
+    if (read_uint32(bs, info_begin) != 0x100) {
         goto fail;
     }
 
-    count = read_uint32(s->fd, info_begin + 4);
+    count = read_uint32(bs, info_begin + 4);
     if (count == 0) {
         goto fail;
     }
@@ -117,12 +113,12 @@ static int dmg_open(BlockDriverState *bs
     while (offset < info_end) {
         uint32_t type;
 
-       count = read_uint32(s->fd, offset);
+       count = read_uint32(bs, offset);
        if(count==0)
            goto fail;
         offset += 4;
 
-       type = read_uint32(s->fd, offset);
+       type = read_uint32(bs, offset);
        if (type == 0x6d697368 && count >= 244) {
            int new_size, chunk_count;
 
@@ -138,7 +134,7 @@ static int dmg_open(BlockDriverState *bs
            s->sectorcounts = qemu_realloc(s->sectorcounts, new_size);
 
            for(i=s->n_chunks;i<s->n_chunks+chunk_count;i++) {
-               s->types[i] = read_uint32(s->fd, offset);
+               s->types[i] = read_uint32(bs, offset);
                offset += 4;
                if(s->types[i]!=0x80000005 && s->types[i]!=1 && s->types[i]!=2) 
{
                    if(s->types[i]==0xffffffff) {
@@ -150,19 +146,19 @@ static int dmg_open(BlockDriverState *bs
                    offset += 36;
                    continue;
                }
-               read_uint32(s->fd, offset);
+               read_uint32(bs, offset);
                offset += 4;
 
-               s->sectors[i] = last_out_offset+read_off(s->fd, offset);
+               s->sectors[i] = last_out_offset+read_off(bs, offset);
                offset += 8;
 
-               s->sectorcounts[i] = read_off(s->fd, offset);
+               s->sectorcounts[i] = read_off(bs, offset);
                offset += 8;
 
-               s->offsets[i] = last_in_offset+read_off(s->fd, offset);
+               s->offsets[i] = last_in_offset+read_off(bs, offset);
                offset += 8;
 
-               s->lengths[i] = read_off(s->fd, offset);
+               s->lengths[i] = read_off(bs, offset);
                offset += 8;
 
                if(s->lengths[i]>max_compressed_size)
@@ -184,7 +180,6 @@ static int dmg_open(BlockDriverState *bs
 
     return 0;
 fail:
-    close(s->fd);
     return -1;
 }
 
@@ -214,8 +209,10 @@ static inline uint32_t search_chunk(BDRV
     return s->n_chunks; /* error */
 }
 
-static inline int dmg_read_chunk(BDRVDMGState *s,int sector_num)
+static inline int dmg_read_chunk(BlockDriverState *bs, int sector_num)
 {
+    BDRVDMGState *s = bs->opaque;
+
     if(!is_sector_in_chunk(s,s->current_chunk,sector_num)) {
        int ret;
        uint32_t chunk = search_chunk(s,sector_num);
@@ -232,8 +229,8 @@ static inline int dmg_read_chunk(BDRVDMG
             * inflated. */
            i=0;
            do {
-               ret = pread(s->fd, s->compressed_chunk+i, s->lengths[chunk]-i,
-                            s->offsets[chunk]);
+               ret = bdrv_pread(bs->file, s->offsets[chunk],
+                                 s->compressed_chunk+i, s->lengths[chunk]-i);
                if(ret<0 && errno==EINTR)
                    ret=0;
                i+=ret;
@@ -254,8 +251,8 @@ static inline int dmg_read_chunk(BDRVDMG
                return -1;
            break; }
        case 1: /* copy */
-           ret = pread(s->fd, s->uncompressed_chunk, s->lengths[chunk],
-                        s->offsets[chunk]);
+           ret = bdrv_pread(bs->file, s->offsets[chunk],
+                             s->uncompressed_chunk, s->lengths[chunk]);
            if (ret != s->lengths[chunk])
                return -1;
            break;
@@ -276,7 +273,7 @@ static int dmg_read(BlockDriverState *bs
 
     for(i=0;i<nb_sectors;i++) {
        uint32_t sector_offset_in_chunk;
-       if(dmg_read_chunk(s, sector_num+i) != 0)
+       if(dmg_read_chunk(bs, sector_num+i) != 0)
            return -1;
        sector_offset_in_chunk = sector_num+i-s->sectors[s->current_chunk];
        memcpy(buf+i*512,s->uncompressed_chunk+sector_offset_in_chunk*512,512);
@@ -287,7 +284,6 @@ static int dmg_read(BlockDriverState *bs
 static void dmg_close(BlockDriverState *bs)
 {
     BDRVDMGState *s = bs->opaque;
-    close(s->fd);
     if(s->n_chunks>0) {
        free(s->types);
        free(s->offsets);
@@ -304,7 +300,7 @@ static BlockDriver bdrv_dmg = {
     .format_name       = "dmg",
     .instance_size     = sizeof(BDRVDMGState),
     .bdrv_probe                = dmg_probe,
-    .bdrv_file_open    = dmg_open,
+    .bdrv_open         = dmg_open,
     .bdrv_read         = dmg_read,
     .bdrv_close                = dmg_close,
 };