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dmg: use pread

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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 <hch@lst.de>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Christoph Hellwig 2010-05-12 16:31:35 +02:00 committed by Kevin Wolf
parent cd02a24b61
commit 16cdf7ce1a
1 changed files with 51 additions and 37 deletions
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88
block/dmg.c
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@ -58,18 +58,18 @@ static int dmg_probe(const uint8_t *buf, int buf_size, const char *filename)
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, const char *filename, int flags)
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, const char *filename, int flags)
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, const char *filename, int flags)
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, const char *filename, int flags)
}
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(BDRVDMGState *s,int sector_num)
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;