Use pread instead of lseek + read in preparation of using the qemu
block API. Note that dmg actually uses the implicit file offset
a lot in dmg_open, and we had to replace it with an offset variable.
Signed-off-by: Christoph Hellwig <h...@lst.de>
Index: qemu-kevin/block/dmg.c
===================================================================
--- qemu-kevin.orig/block/dmg.c 2010-05-12 16:19:59.586012160 +0200
+++ qemu-kevin/block/dmg.c 2010-05-12 16:23:07.510005522 +0200
@@ -58,18 +58,18 @@ static int dmg_probe(const uint8_t *buf,
return 0;
}
-static off_t read_off(int fd)
+static off_t read_off(int fd, int64_t offset)
{
uint64_t buffer;
- if(read(fd,&buffer,8)<8)
+ if (pread(fd, &buffer, 8, offset) < 8)
return 0;
return be64_to_cpu(buffer);
}
-static off_t read_uint32(int fd)
+static off_t read_uint32(int fd, int64_t offset)
{
uint32_t buffer;
- if(read(fd,&buffer,4)<4)
+ if (pread(fd, &buffer, 4, offset) < 4)
return 0;
return be32_to_cpu(buffer);
}
@@ -80,6 +80,7 @@ static int dmg_open(BlockDriverState *bs
off_t info_begin,info_end,last_in_offset,last_out_offset;
uint32_t count;
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)
@@ -89,38 +90,45 @@ static int dmg_open(BlockDriverState *bs
s->offsets = s->lengths = s->sectors = s->sectorcounts = NULL;
/* read offset of info blocks */
- if(lseek(s->fd,-0x1d8,SEEK_END)<0) {
+ offset = lseek(s->fd, -0x1d8, SEEK_END);
+ if (offset < 0) {
goto fail;
}
- info_begin=read_off(s->fd);
- if(info_begin==0)
- goto fail;
- if(lseek(s->fd,info_begin,SEEK_SET)<0)
- goto fail;
- if(read_uint32(s->fd)!=0x100)
- goto fail;
- if((count = read_uint32(s->fd))==0)
- goto fail;
- info_end = info_begin+count;
- if(lseek(s->fd,0xf8,SEEK_CUR)<0)
+ info_begin = read_off(s->fd, offset);
+ if (info_begin == 0) {
goto fail;
+ }
+
+ if (read_uint32(s->fd, info_begin) != 0x100) {
+ goto fail;
+ }
+
+ count = read_uint32(s->fd, info_begin + 4);
+ if (count == 0) {
+ goto fail;
+ }
+ info_end = info_begin + count;
+
+ offset = info_begin + 0x100;
/* read offsets */
last_in_offset = last_out_offset = 0;
- while(lseek(s->fd,0,SEEK_CUR)<info_end) {
+ while (offset < info_end) {
uint32_t type;
- count = read_uint32(s->fd);
+ count = read_uint32(s->fd, offset);
if(count==0)
goto fail;
- type = read_uint32(s->fd);
- if(type!=0x6d697368 || count<244)
- lseek(s->fd,count-4,SEEK_CUR);
- else {
+ offset += 4;
+
+ type = read_uint32(s->fd, offset);
+ if (type == 0x6d697368 && count >= 244) {
int new_size, chunk_count;
- if(lseek(s->fd,200,SEEK_CUR)<0)
- goto fail;
+
+ offset += 4;
+ offset += 200;
+
chunk_count = (count-204)/40;
new_size = sizeof(uint64_t) * (s->n_chunks + chunk_count);
s->types = qemu_realloc(s->types, new_size/2);
@@ -130,7 +138,8 @@ 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);
+ s->types[i] = read_uint32(s->fd, offset);
+ offset += 4;
if(s->types[i]!=0x80000005 && s->types[i]!=1 && s->types[i]!=2)
{
if(s->types[i]==0xffffffff) {
last_in_offset = s->offsets[i-1]+s->lengths[i-1];
@@ -138,15 +147,23 @@ static int dmg_open(BlockDriverState *bs
}
chunk_count--;
i--;
- if(lseek(s->fd,36,SEEK_CUR)<0)
- goto fail;
+ offset += 36;
continue;
}
- read_uint32(s->fd);
- s->sectors[i] = last_out_offset+read_off(s->fd);
- s->sectorcounts[i] = read_off(s->fd);
- s->offsets[i] = last_in_offset+read_off(s->fd);
- s->lengths[i] = read_off(s->fd);
+ offset += 4;
+
+ s->sectors[i] = last_out_offset+read_off(s->fd, offset);
+ offset += 8;
+
+ s->sectorcounts[i] = read_off(s->fd, offset);
+ offset += 8;
+
+ s->offsets[i] = last_in_offset+read_off(s->fd, offset);
+ offset += 8;
+
+ s->lengths[i] = read_off(s->fd, offset);
+ offset += 8;
+
if(s->lengths[i]>max_compressed_size)
max_compressed_size = s->lengths[i];
if(s->sectorcounts[i]>max_sectors_per_chunk)
@@ -210,15 +227,12 @@ static inline int dmg_read_chunk(BDRVDMG
case 0x80000005: { /* zlib compressed */
int i;
- ret = lseek(s->fd, s->offsets[chunk], SEEK_SET);
- if(ret<0)
- return -1;
-
/* we need to buffer, because only the chunk as whole can be
* inflated. */
i=0;
do {
- ret = read(s->fd, s->compressed_chunk+i, s->lengths[chunk]-i);
+ ret = pread(s->fd, s->compressed_chunk+i, s->lengths[chunk]-i,
+ s->offsets[chunk] + i);
if(ret<0 && errno==EINTR)
ret=0;
i+=ret;
