Gao, just returned from holidays. Let me rethink about this approach.
--Pratik On Wed, Dec 11, 2019, 11:14 AM Gao Xiang <[email protected]> wrote: > On Mon, Dec 09, 2019 at 03:18:17PM +0800, Gao Xiang wrote: > > Hi Pratik, > > > > On Mon, Dec 09, 2019 at 12:34:50PM +0530, Pratik Shinde wrote: > > > Hello Gao, > > > > > > Did you get any chance to look at this in detail. > > > > I looked into your implementation weeks before. > > > > As my reply in the previous email, did you see it and could you check it > out? > > > > Kernel emails are not top-posting so you could scroll down to the end. > > > > > > "variable-sized inode" isn't a problem here, which can be handled > > > > similar to the case of "compress indexes". > > > > > > > > Probably no need to write linked list to the disk but generate > linked list > > > > in memory when writing data on the fly, and then transfer to a > > > > variable-sized > > > > extent array at the time of writing inode metadata (The order is > firstly > > > > data > > > > and then metadata in erofs-utils so it looks practical.) > > > Some feedback words here? Do you think it is unnecessary to use such > array for limited fragmented holes (either in-memory or ondisk) as well? > > Thanks, > Gao Xiang > > > > > > Thanks, > > Gao Xiang > > > > > > > > --Pratik. > > > > > > On Wed, Dec 4, 2019, 7:52 AM Gao Xiang <[email protected]> wrote: > > > > > > > Hi Pratik, > > > > > > > > I'll give detailed words this weekend if you have more questions > > > > since I'm busying in other stupid intra-company stuffs now... > > > > > > > > On Tue, Dec 03, 2019 at 07:32:50PM +0530, Pratik Shinde wrote: > > > > > NOTE: The patch is not fully complete yet, with this patch I just > want to > > > > > present rough idea of what I am trying to achieve. > > > > > > > > > > The patch does following : > > > > > 1) Detect holes (of size EROFS_BLKSIZ) in uncompressed files. > > > > > 2) Keep track of holes per file. > > > > > > > > > > In-order to track holes, I used an array of size = (file_size / > > > > blocksize) > > > > > The array basically tracks number of holes before a particular > logical > > > > file block. > > > > > e.g blks[i] = 10 meaning ith block has 10 holes before it. > > > > > If a particular block is a hole we set the index to '-1'. > > > > > > > > > > how read logic will change: > > > > > 1) currently we simply map read offset to a fs block. > > > > > 2) with holes in place the calculation of block number would be: > > > > > > > > > > blkno = start_block + (offset >> block_size_shift) - (number of > > > > > holes before > > > > block in which offset falls) > > > > > > > > > > 3) If a read offset falls inside a hole (which can be found using > above > > > > array). We > > > > > fill the user buffer with '\0' on the fly. > > > > > > > > > > through this,block no. lookup would still be performed in constant > time. > > > > > > > > > > The biggest problem with this approach is - we have to store the > hole > > > > tracking > > > > > array for every file to the disk.Which doesn't seems to be > practical.we > > > > can use a linkedlist, > > > > > but that will make size of inode variable. > > > > > > > > "variable-sized inode" isn't a problem here, which can be handled > > > > similar to the case of "compress indexes". > > > > > > > > Probably no need to write linked list to the disk but generate > linked list > > > > in memory when writing data on the fly, and then transfer to a > > > > variable-sized > > > > extent array at the time of writing inode metadata (The order is > firstly > > > > data > > > > and then metadata in erofs-utils so it looks practical.) > > > > > > > > Thanks, > > > > Gao Xiang > > > > > > > > > > > > > > Signed-off-by: Pratik Shinde <[email protected]> > > > > > --- > > > > > lib/inode.c | 67 > > > > ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++- > > > > > 1 file changed, 66 insertions(+), 1 deletion(-) > > > > > > > > > > diff --git a/lib/inode.c b/lib/inode.c > > > > > index 0e19b11..af31949 100644 > > > > > --- a/lib/inode.c > > > > > +++ b/lib/inode.c > > > > > @@ -38,6 +38,61 @@ static unsigned char erofs_type_by_mode[S_IFMT > >> > > > > S_SHIFT] = { > > > > > > > > > > struct list_head inode_hashtable[NR_INODE_HASHTABLE]; > > > > > > > > > > + > > > > > +#define IS_HOLE(start, end) (roundup(start, EROFS_BLKSIZ) == > start && > > > > \ > > > > > + roundup(end, EROFS_BLKSIZ) == end && > \ > > > > > + (end - start) % EROFS_BLKSIZ == 0) > > > > > +#define HOLE_BLK -1 > > > > > +unsigned int erofs_detect_holes(struct erofs_inode *inode, int > *blks) > > > > > +{ > > > > > + int i, fd, st, en; > > > > > + unsigned int nblocks; > > > > > + erofs_off_t data, hole, len; > > > > > + > > > > > + nblocks = inode->i_size / EROFS_BLKSIZ; > > > > > + for (i = 0; i < nblocks; i++) > > > > > + blks[i] = 0; > > > > > + fd = open(inode->i_srcpath, O_RDONLY); > > > > > + if (fd < 0) { > > > > > + return -errno; > > > > > + } > > > > > + len = lseek(fd, 0, SEEK_END); > > > > > + if (lseek(fd, 0, SEEK_SET) == -1) > > > > > + return -errno; > > > > > + data = 0; > > > > > + while (data < len) { > > > > > + hole = lseek(fd, data, SEEK_HOLE); > > > > > + if (hole == len) > > > > > + break; > > > > > + data = lseek(fd, hole, SEEK_DATA); > > > > > + if (data < 0 || hole > data) { > > > > > + return -EINVAL; > > > > > + } > > > > > + if (IS_HOLE(hole, data)) { > > > > > + st = hole >> S_SHIFT; > > > > > + en = data >> S_SHIFT; > > > > > + nblocks -= (en - st); > > > > > + for (i = st; i < en; i++) > > > > > + blks[i] = HOLE_BLK; > > > > > + } > > > > > + } > > > > > + return nblocks; > > > > > +} > > > > > + > > > > > +int erofs_fill_holedata(int *blks, unsigned int nblocks) { > > > > > + int i, nholes = 0; > > > > > + for (i = 0; i < nblocks; i++) { > > > > > + if (blks[i] == -1) > > > > > + nholes++; > > > > > + else { > > > > > + blks[i] = nholes; > > > > > + if (nholes >= (i + 1)) > > > > > + return -EINVAL; > > > > > + } > > > > > + } > > > > > + return 0; > > > > > +} > > > > > + > > > > > void erofs_inode_manager_init(void) > > > > > { > > > > > unsigned int i; > > > > > @@ -305,6 +360,7 @@ static bool erofs_file_is_compressible(struct > > > > erofs_inode *inode) > > > > > int erofs_write_file(struct erofs_inode *inode) > > > > > { > > > > > unsigned int nblocks, i; > > > > > + int *blks; > > > > > int ret, fd; > > > > > > > > > > if (!inode->i_size) { > > > > > @@ -322,7 +378,13 @@ int erofs_write_file(struct erofs_inode > *inode) > > > > > /* fallback to all data uncompressed */ > > > > > inode->datalayout = EROFS_INODE_FLAT_INLINE; > > > > > nblocks = inode->i_size / EROFS_BLKSIZ; > > > > > - > > > > > + blks = malloc(sizeof(int) * nblocks); > > > > > + nblocks = erofs_detect_holes(inode, blks); > > > > > + if (nblocks < 0) > > > > > + return nblocks; > > > > > + if ((ret = erofs_fill_holedata(blks, nblocks)) != 0) { > > > > > + return ret; > > > > > + } > > > > > ret = __allocate_inode_bh_data(inode, nblocks); > > > > > if (ret) > > > > > return ret; > > > > > @@ -332,6 +394,8 @@ int erofs_write_file(struct erofs_inode *inode) > > > > > return -errno; > > > > > > > > > > for (i = 0; i < nblocks; ++i) { > > > > > + if (blks[i] == HOLE_BLK) > > > > > + continue; > > > > > char buf[EROFS_BLKSIZ]; > > > > > > > > > > ret = read(fd, buf, EROFS_BLKSIZ); > > > > > @@ -962,3 +1026,4 @@ struct erofs_inode > > > > *erofs_mkfs_build_tree_from_path(struct erofs_inode *parent, > > > > > return erofs_mkfs_build_tree(inode); > > > > > } > > > > > > > > > > + > > > > > -- > > > > > 2.9.3 > > > > > > > > > >
