Message ID | 20100507145603.GB14245@lst.de |
---|---|
State | New |
Headers | show |
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 <hch@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
On Mon, May 10, 2010 at 12:07:40PM +0200, Kevin Wolf wrote: > > > > - 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? Yeah, should be 0x100. That's what you get for quickly doing hex calculation in your head. > > + 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? I don't think so. For that case we previously did a lseek(s->fd,count-4,SEEK_CUR) to undo the 4 byte advance done by the read. > > - 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. Thanks, fixed. > > /* 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. You're right. The EINTR check confused me an I took this for just retrying reads on EINTR. Now this code i quite nasty for error returns except EINTR because we'll subtract one from the i loop iteration, yikes. I'll just reuse the i variable to keep the same kind of bug for both sides of the equation. God, do I hate this code..
Am 10.05.2010 22:20, schrieb Christoph Hellwig: > On Mon, May 10, 2010 at 12:07:40PM +0200, Kevin Wolf wrote: >>> + 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? > > I don't think so. For that case we previously did a > > lseek(s->fd,count-4,SEEK_CUR) > > to undo the 4 byte advance done by the read. You're right. Somehow I completely missed the original then branch and that you changed the condition. Kevin
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; - 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 + 0xfc; /* 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 +147,24 @@ 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); + 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]); if(ret<0 && errno==EINTR) ret=0; i+=ret;
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>