Am 07.05.2010 16:56, schrieb Christoph Hellwig:
> 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 2010-05-03 13:17:40.696287171 +0200
> +++ qemu-kevin/block/dmg.c 2010-05-03 13:29:39.560024006 +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;
We seek to info_begin.
> - if(read_uint32(s->fd)!=0x100)
> - goto fail;
Now we are at info_begin + 4
> - if((count = read_uint32(s->fd))==0)
> - goto fail;
info_begin + 8
> - info_end = info_begin+count;
> - if(lseek(s->fd,0xf8,SEEK_CUR)<0)
info_begin + 0x100
> + 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 + 0xfc;
So, wrong offset here?
>
> /* 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;
Isn't this needed in the else case, too?
> + 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 +147,24 @@ 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);
> + read_uint32(s->fd, offset);
This read is useless. offset += 4 alone should be enough.
> + 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 +228,12 @@ 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]);
This is in a loop, whereas the lseek was outside the loop. From the
second iteration on you'll repeat the first read instead of advancing.
Kevin
