From c8c0df241cc2719b1262e627f999638411934f60 Mon Sep 17 00:00:00 2001 From: Zheng Liu Date: Thu, 8 Nov 2012 21:57:40 -0500 Subject: [PATCH] ext4: introduce lseek SEEK_DATA/SEEK_HOLE support This patch makes ext4 really support SEEK_DATA/SEEK_HOLE flags. Block-mapped and extent-mapped files are fully implemented together because ext4_map_blocks hides this differences. After applying this patch, it will cause a failure in xfstest #285 when the file is block-mapped due to block-mapped file isn't support fallocate(2). I had tried to use ext4_ext_walk_space() to retrieve the offset for a extent-mapped file. But finally I decide to keep using ext4_map_blocks() to support SEEK_DATA/SEEK_HOLE because ext4_map_blocks() can hide the difference between block-mapped file and extent-mapped file. Moreover, in next step, extent status tree will track all extent status, and we can get all mappings from this tree. So I think that using ext4_map_blocks() is a better choice. CC: Hugh Dickins Signed-off-by: Jie Liu Signed-off-by: Zheng Liu Signed-off-by: "Theodore Ts'o" --- fs/ext4/file.c | 334 ++++++++++++++++++++++++++++++++++++++++++++++++- 1 file changed, 332 insertions(+), 2 deletions(-) diff --git a/fs/ext4/file.c b/fs/ext4/file.c index bf3966bccd34..2f5759eb9f89 100644 --- a/fs/ext4/file.c +++ b/fs/ext4/file.c @@ -24,6 +24,7 @@ #include #include #include +#include #include "ext4.h" #include "ext4_jbd2.h" #include "xattr.h" @@ -285,6 +286,324 @@ static int ext4_file_open(struct inode * inode, struct file * filp) return dquot_file_open(inode, filp); } +/* + * Here we use ext4_map_blocks() to get a block mapping for a extent-based + * file rather than ext4_ext_walk_space() because we can introduce + * SEEK_DATA/SEEK_HOLE for block-mapped and extent-mapped file at the same + * function. When extent status tree has been fully implemented, it will + * track all extent status for a file and we can directly use it to + * retrieve the offset for SEEK_DATA/SEEK_HOLE. + */ + +/* + * When we retrieve the offset for SEEK_DATA/SEEK_HOLE, we would need to + * lookup page cache to check whether or not there has some data between + * [startoff, endoff] because, if this range contains an unwritten extent, + * we determine this extent as a data or a hole according to whether the + * page cache has data or not. + */ +static int ext4_find_unwritten_pgoff(struct inode *inode, + int origin, + struct ext4_map_blocks *map, + loff_t *offset) +{ + struct pagevec pvec; + unsigned int blkbits; + pgoff_t index; + pgoff_t end; + loff_t endoff; + loff_t startoff; + loff_t lastoff; + int found = 0; + + blkbits = inode->i_sb->s_blocksize_bits; + startoff = *offset; + lastoff = startoff; + endoff = (map->m_lblk + map->m_len) << blkbits; + + index = startoff >> PAGE_CACHE_SHIFT; + end = endoff >> PAGE_CACHE_SHIFT; + + pagevec_init(&pvec, 0); + do { + int i, num; + unsigned long nr_pages; + + num = min_t(pgoff_t, end - index, PAGEVEC_SIZE); + nr_pages = pagevec_lookup(&pvec, inode->i_mapping, index, + (pgoff_t)num); + if (nr_pages == 0) { + if (origin == SEEK_DATA) + break; + + BUG_ON(origin != SEEK_HOLE); + /* + * If this is the first time to go into the loop and + * offset is not beyond the end offset, it will be a + * hole at this offset + */ + if (lastoff == startoff || lastoff < endoff) + found = 1; + break; + } + + /* + * If this is the first time to go into the loop and + * offset is smaller than the first page offset, it will be a + * hole at this offset. + */ + if (lastoff == startoff && origin == SEEK_HOLE && + lastoff < page_offset(pvec.pages[0])) { + found = 1; + break; + } + + for (i = 0; i < nr_pages; i++) { + struct page *page = pvec.pages[i]; + struct buffer_head *bh, *head; + + /* + * If the current offset is not beyond the end of given + * range, it will be a hole. + */ + if (lastoff < endoff && origin == SEEK_HOLE && + page->index > end) { + found = 1; + *offset = lastoff; + goto out; + } + + lock_page(page); + + if (unlikely(page->mapping != inode->i_mapping)) { + unlock_page(page); + continue; + } + + if (!page_has_buffers(page)) { + unlock_page(page); + continue; + } + + if (page_has_buffers(page)) { + lastoff = page_offset(page); + bh = head = page_buffers(page); + do { + if (buffer_uptodate(bh) || + buffer_unwritten(bh)) { + if (origin == SEEK_DATA) + found = 1; + } else { + if (origin == SEEK_HOLE) + found = 1; + } + if (found) { + *offset = max_t(loff_t, + startoff, lastoff); + unlock_page(page); + goto out; + } + lastoff += bh->b_size; + bh = bh->b_this_page; + } while (bh != head); + } + + lastoff = page_offset(page) + PAGE_SIZE; + unlock_page(page); + } + + /* + * The no. of pages is less than our desired, that would be a + * hole in there. + */ + if (nr_pages < num && origin == SEEK_HOLE) { + found = 1; + *offset = lastoff; + break; + } + + index = pvec.pages[i - 1]->index + 1; + pagevec_release(&pvec); + } while (index <= end); + +out: + pagevec_release(&pvec); + return found; +} + +/* + * ext4_seek_data() retrieves the offset for SEEK_DATA. + */ +static loff_t ext4_seek_data(struct file *file, loff_t offset, loff_t maxsize) +{ + struct inode *inode = file->f_mapping->host; + struct ext4_map_blocks map; + struct extent_status es; + ext4_lblk_t start, last, end; + loff_t dataoff, isize; + int blkbits; + int ret = 0; + + mutex_lock(&inode->i_mutex); + + isize = i_size_read(inode); + if (offset >= isize) { + mutex_unlock(&inode->i_mutex); + return -ENXIO; + } + + blkbits = inode->i_sb->s_blocksize_bits; + start = offset >> blkbits; + last = start; + end = isize >> blkbits; + dataoff = offset; + + do { + map.m_lblk = last; + map.m_len = end - last + 1; + ret = ext4_map_blocks(NULL, inode, &map, 0); + if (ret > 0 && !(map.m_flags & EXT4_MAP_UNWRITTEN)) { + if (last != start) + dataoff = last << blkbits; + break; + } + + /* + * If there is a delay extent at this offset, + * it will be as a data. + */ + es.start = last; + (void)ext4_es_find_extent(inode, &es); + if (last >= es.start && + last < es.start + es.len) { + if (last != start) + dataoff = last << blkbits; + break; + } + + /* + * If there is a unwritten extent at this offset, + * it will be as a data or a hole according to page + * cache that has data or not. + */ + if (map.m_flags & EXT4_MAP_UNWRITTEN) { + int unwritten; + unwritten = ext4_find_unwritten_pgoff(inode, SEEK_DATA, + &map, &dataoff); + if (unwritten) + break; + } + + last++; + dataoff = last << blkbits; + } while (last <= end); + + mutex_unlock(&inode->i_mutex); + + if (dataoff > isize) + return -ENXIO; + + if (dataoff < 0 && !(file->f_mode & FMODE_UNSIGNED_OFFSET)) + return -EINVAL; + if (dataoff > maxsize) + return -EINVAL; + + if (dataoff != file->f_pos) { + file->f_pos = dataoff; + file->f_version = 0; + } + + return dataoff; +} + +/* + * ext4_seek_hole() retrieves the offset for SEEK_HOLE. + */ +static loff_t ext4_seek_hole(struct file *file, loff_t offset, loff_t maxsize) +{ + struct inode *inode = file->f_mapping->host; + struct ext4_map_blocks map; + struct extent_status es; + ext4_lblk_t start, last, end; + loff_t holeoff, isize; + int blkbits; + int ret = 0; + + mutex_lock(&inode->i_mutex); + + isize = i_size_read(inode); + if (offset >= isize) { + mutex_unlock(&inode->i_mutex); + return -ENXIO; + } + + blkbits = inode->i_sb->s_blocksize_bits; + start = offset >> blkbits; + last = start; + end = isize >> blkbits; + holeoff = offset; + + do { + map.m_lblk = last; + map.m_len = end - last + 1; + ret = ext4_map_blocks(NULL, inode, &map, 0); + if (ret > 0 && !(map.m_flags & EXT4_MAP_UNWRITTEN)) { + last += ret; + holeoff = last << blkbits; + continue; + } + + /* + * If there is a delay extent at this offset, + * we will skip this extent. + */ + es.start = last; + (void)ext4_es_find_extent(inode, &es); + if (last >= es.start && + last < es.start + es.len) { + last = es.start + es.len; + holeoff = last << blkbits; + continue; + } + + /* + * If there is a unwritten extent at this offset, + * it will be as a data or a hole according to page + * cache that has data or not. + */ + if (map.m_flags & EXT4_MAP_UNWRITTEN) { + int unwritten; + unwritten = ext4_find_unwritten_pgoff(inode, SEEK_HOLE, + &map, &holeoff); + if (!unwritten) { + last += ret; + holeoff = last << blkbits; + continue; + } + } + + /* find a hole */ + break; + } while (last <= end); + + mutex_unlock(&inode->i_mutex); + + if (holeoff > isize) + holeoff = isize; + + if (holeoff < 0 && !(file->f_mode & FMODE_UNSIGNED_OFFSET)) + return -EINVAL; + if (holeoff > maxsize) + return -EINVAL; + + if (holeoff != file->f_pos) { + file->f_pos = holeoff; + file->f_version = 0; + } + + return holeoff; +} + /* * ext4_llseek() handles both block-mapped and extent-mapped maxbytes values * by calling generic_file_llseek_size() with the appropriate maxbytes @@ -300,8 +619,19 @@ loff_t ext4_llseek(struct file *file, loff_t offset, int origin) else maxbytes = inode->i_sb->s_maxbytes; - return generic_file_llseek_size(file, offset, origin, - maxbytes, i_size_read(inode)); + switch (origin) { + case SEEK_SET: + case SEEK_CUR: + case SEEK_END: + return generic_file_llseek_size(file, offset, origin, + maxbytes, i_size_read(inode)); + case SEEK_DATA: + return ext4_seek_data(file, offset, maxbytes); + case SEEK_HOLE: + return ext4_seek_hole(file, offset, maxbytes); + } + + return -EINVAL; } const struct file_operations ext4_file_operations = { -- 2.20.1