On 2015-02-24 at 01:44, Peter Lieven wrote:
Am 23.02.2015 um 19:29 schrieb Max Reitz:On 2015-02-23 at 09:27, Peter Lieven wrote:Signed-off-by: Peter Lieven <p...@kamp.de> ---block/vpc.c | 116 +++++++++++++++++++++++++++--------------------------------1 file changed, 52 insertions(+), 64 deletions(-)diff --git a/block/vpc.c b/block/vpc.c index 326c2bb..4e5ba85 100644 --- a/block/vpc.c +++ b/block/vpc.c@@ -497,40 +497,70 @@ static int vpc_get_info(BlockDriverState *bs, BlockDriverInfo *bdi)return 0; } -static int vpc_read(BlockDriverState *bs, int64_t sector_num, - uint8_t *buf, int nb_sectors)+static int64_t coroutine_fn vpc_co_get_block_status(BlockDriverState *bs,+ int64_t sector_num, int nb_sectors, int *pnum)How about just putting the function header here? If you really have to move vpc_co_get_block_status() up, I'd rather like it to be in a separate patch.Second, while apparently vpc_read() is actually called in a coroutine, that is pretty hard to know. Most importantly, it's not marked as a coroutine_fn. Therefore I don't think it's a good idea to call vpc_co_get_block_status() directly; I'd vote for either using bdrv_get_block_status(), or moving the content of vpc_co_get_block_status() to a non-coroutine_fn (it doesn't contain an coroutine-related function calls, so this is fine) and then making vpc_co_get_block_status() a wrapper around that, or just dropping this patch.The latter I'm proposing because I don't really see what this patch improves. The previous vpc_read() function was pretty straightforward, too, and I don't think it was unbearably longer.One could argue that the coroutine_fn stuff doesn't really matter in this situation because it doesn't actually do anything right now and vpc_co_get_block_status() does not call any other coroutine_fn functions in turn; however, it is a semantic contract established by include/block/coroutine.h and as far as I remember, Stefan did eventually want to have something to error out on compile-time if a non-coroutine_fn function calls a coroutine_fn. I don't like breaking this contract even if it's not bad in this specific case.Considering you probably think bdrv_get_block_status() to be too much overhead (it will fall down to the protocol layer on VHD_FIXED) and you probably find making vpc_read() shorter justified (again, which I don't necessarily), I think moving the contents of vpc_co_get_block_status() to a non-coroutine_fn might be the best way to go.{ BDRVVPCState *s = bs->opaque; - int ret; - int64_t offset; - int64_t sectors, sectors_per_block; - VHDFooter *footer = (VHDFooter *) s->footer_buf; + VHDFooter *footer = (VHDFooter*) s->footer_buf; + int64_t start, offset; + bool allocated; + int n; if (be32_to_cpu(footer->type) == VHD_FIXED) { - return bdrv_read(bs->file, sector_num, buf, nb_sectors); + *pnum = nb_sectors;+ return BDRV_BLOCK_RAW | BDRV_BLOCK_OFFSET_VALID | BDRV_BLOCK_DATA |+ (sector_num << BDRV_SECTOR_BITS); } - while (nb_sectors > 0) { - offset = get_sector_offset(bs, sector_num, 0); - sectors_per_block = s->block_size >> BDRV_SECTOR_BITS;- sectors = sectors_per_block - (sector_num % sectors_per_block);- if (sectors > nb_sectors) { - sectors = nb_sectors; + offset = get_sector_offset(bs, sector_num, 0); + start = offset; + allocated = (offset != -1); + *pnum = 0; + + do {+ /* All sectors in a block are contiguous (without using the bitmap) */+ n = ROUND_UP(sector_num + 1, s->block_size / BDRV_SECTOR_SIZE) + - sector_num; + n = MIN(n, nb_sectors); + + *pnum += n; + sector_num += n; + nb_sectors -= n; + + if (allocated) { + return BDRV_BLOCK_DATA | BDRV_BLOCK_OFFSET_VALID | start; } + if (nb_sectors == 0) { + break; + } + offset = get_sector_offset(bs, sector_num, 0); + } while (offset == -1); - if (offset == -1) { - memset(buf, 0, sectors * BDRV_SECTOR_SIZE); - } else { - ret = bdrv_pread(bs->file, offset, buf, - sectors * BDRV_SECTOR_SIZE); - if (ret != sectors * BDRV_SECTOR_SIZE) { + return 0; +} + +static int vpc_read(BlockDriverState *bs, int64_t sector_num, + uint8_t *buf, int nb_sectors) +{ + int ret, n; + int64_t ret2; + + while (nb_sectors > 0) {+ ret2 = vpc_co_get_block_status(bs, sector_num, nb_sectors, &n);+Superfluous whitespace here.+ if (ret2 & BDRV_BLOCK_OFFSET_VALID) { + ret = bdrv_pread(bs->file, ret2 & BDRV_SECTOR_MASK, buf, + n * BDRV_SECTOR_SIZE); + if (ret != n * BDRV_SECTOR_SIZE) { return -1;Please make that "return ret" (and possibly "if (ret < 0)", if you want to).I took this from the orignal vpc_read function. Maybe the author also wantedto catch short reads.
There are no short reads (any more), though. ;-)
I tend to drop the whole patch anyway. I was tempted to use that new vpc_co_get_block_status function somehow because I saw that part of its logic is in vpc_read as well.If it should stay maybe it would be an option to inline vpc_read in vpc_co_read (and the same for write)?
Oh, I totally missed the vpc_co_read(). That would make sense, because you actually can call vpc_co_get_block_status() from there, or you just add the coroutine_fn specifier to vpc_read(). It's up to you, I'm fine with all of dropping, inlining, and making vpc_read() a coroutine_fn.
Max
