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 <hughd@google.com> Signed-off-by: Jie Liu <jeff.liu@oracle.com> Signed-off-by: Zheng Liu <wenqing.lz@taobao.com> Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
This commit is contained in:
Zheng Liu
Theodore Ts'o
parent
b3aff3e3f6
commit
c8c0df241c
334
fs/ext4/file.c
334
fs/ext4/file.c
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@ -24,6 +24,7 @@
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#include <linux/mount.h>
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#include <linux/path.h>
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#include <linux/quotaops.h>
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#include <linux/pagevec.h>
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#include "ext4.h"
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#include "ext4_jbd2.h"
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#include "xattr.h"
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@ -285,6 +286,324 @@ static int ext4_file_open(struct inode * inode, struct file * filp)
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return dquot_file_open(inode, filp);
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}
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/*
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* Here we use ext4_map_blocks() to get a block mapping for a extent-based
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* file rather than ext4_ext_walk_space() because we can introduce
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* SEEK_DATA/SEEK_HOLE for block-mapped and extent-mapped file at the same
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* function. When extent status tree has been fully implemented, it will
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* track all extent status for a file and we can directly use it to
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* retrieve the offset for SEEK_DATA/SEEK_HOLE.
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*/
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/*
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* When we retrieve the offset for SEEK_DATA/SEEK_HOLE, we would need to
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* lookup page cache to check whether or not there has some data between
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* [startoff, endoff] because, if this range contains an unwritten extent,
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* we determine this extent as a data or a hole according to whether the
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* page cache has data or not.
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*/
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static int ext4_find_unwritten_pgoff(struct inode *inode,
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int origin,
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struct ext4_map_blocks *map,
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loff_t *offset)
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{
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struct pagevec pvec;
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unsigned int blkbits;
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pgoff_t index;
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pgoff_t end;
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loff_t endoff;
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loff_t startoff;
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loff_t lastoff;
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int found = 0;
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blkbits = inode->i_sb->s_blocksize_bits;
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startoff = *offset;
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lastoff = startoff;
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endoff = (map->m_lblk + map->m_len) << blkbits;
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index = startoff >> PAGE_CACHE_SHIFT;
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end = endoff >> PAGE_CACHE_SHIFT;
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pagevec_init(&pvec, 0);
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do {
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int i, num;
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unsigned long nr_pages;
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num = min_t(pgoff_t, end - index, PAGEVEC_SIZE);
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nr_pages = pagevec_lookup(&pvec, inode->i_mapping, index,
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(pgoff_t)num);
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if (nr_pages == 0) {
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if (origin == SEEK_DATA)
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break;
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BUG_ON(origin != SEEK_HOLE);
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/*
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* If this is the first time to go into the loop and
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* offset is not beyond the end offset, it will be a
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* hole at this offset
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*/
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if (lastoff == startoff || lastoff < endoff)
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found = 1;
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break;
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}
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/*
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* If this is the first time to go into the loop and
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* offset is smaller than the first page offset, it will be a
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* hole at this offset.
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*/
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if (lastoff == startoff && origin == SEEK_HOLE &&
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lastoff < page_offset(pvec.pages[0])) {
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found = 1;
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break;
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}
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for (i = 0; i < nr_pages; i++) {
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struct page *page = pvec.pages[i];
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struct buffer_head *bh, *head;
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/*
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* If the current offset is not beyond the end of given
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* range, it will be a hole.
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*/
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if (lastoff < endoff && origin == SEEK_HOLE &&
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page->index > end) {
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found = 1;
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*offset = lastoff;
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goto out;
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}
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lock_page(page);
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if (unlikely(page->mapping != inode->i_mapping)) {
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unlock_page(page);
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continue;
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}
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if (!page_has_buffers(page)) {
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unlock_page(page);
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continue;
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}
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if (page_has_buffers(page)) {
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lastoff = page_offset(page);
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bh = head = page_buffers(page);
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do {
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if (buffer_uptodate(bh) ||
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buffer_unwritten(bh)) {
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if (origin == SEEK_DATA)
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found = 1;
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} else {
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if (origin == SEEK_HOLE)
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found = 1;
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}
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if (found) {
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*offset = max_t(loff_t,
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startoff, lastoff);
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unlock_page(page);
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goto out;
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}
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lastoff += bh->b_size;
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bh = bh->b_this_page;
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} while (bh != head);
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}
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lastoff = page_offset(page) + PAGE_SIZE;
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unlock_page(page);
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}
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/*
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* The no. of pages is less than our desired, that would be a
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* hole in there.
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*/
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if (nr_pages < num && origin == SEEK_HOLE) {
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found = 1;
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*offset = lastoff;
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break;
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}
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index = pvec.pages[i - 1]->index + 1;
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pagevec_release(&pvec);
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} while (index <= end);
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out:
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pagevec_release(&pvec);
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return found;
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}
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/*
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* ext4_seek_data() retrieves the offset for SEEK_DATA.
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*/
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static loff_t ext4_seek_data(struct file *file, loff_t offset, loff_t maxsize)
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{
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struct inode *inode = file->f_mapping->host;
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struct ext4_map_blocks map;
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struct extent_status es;
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ext4_lblk_t start, last, end;
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loff_t dataoff, isize;
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int blkbits;
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int ret = 0;
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mutex_lock(&inode->i_mutex);
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isize = i_size_read(inode);
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if (offset >= isize) {
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mutex_unlock(&inode->i_mutex);
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return -ENXIO;
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}
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blkbits = inode->i_sb->s_blocksize_bits;
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start = offset >> blkbits;
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last = start;
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end = isize >> blkbits;
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dataoff = offset;
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do {
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map.m_lblk = last;
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map.m_len = end - last + 1;
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ret = ext4_map_blocks(NULL, inode, &map, 0);
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if (ret > 0 && !(map.m_flags & EXT4_MAP_UNWRITTEN)) {
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if (last != start)
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dataoff = last << blkbits;
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break;
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}
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/*
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* If there is a delay extent at this offset,
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* it will be as a data.
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*/
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es.start = last;
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(void)ext4_es_find_extent(inode, &es);
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if (last >= es.start &&
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last < es.start + es.len) {
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if (last != start)
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dataoff = last << blkbits;
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break;
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}
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/*
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* If there is a unwritten extent at this offset,
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* it will be as a data or a hole according to page
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* cache that has data or not.
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*/
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if (map.m_flags & EXT4_MAP_UNWRITTEN) {
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int unwritten;
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unwritten = ext4_find_unwritten_pgoff(inode, SEEK_DATA,
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&map, &dataoff);
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if (unwritten)
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break;
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}
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last++;
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dataoff = last << blkbits;
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} while (last <= end);
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mutex_unlock(&inode->i_mutex);
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if (dataoff > isize)
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return -ENXIO;
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if (dataoff < 0 && !(file->f_mode & FMODE_UNSIGNED_OFFSET))
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return -EINVAL;
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if (dataoff > maxsize)
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return -EINVAL;
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if (dataoff != file->f_pos) {
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file->f_pos = dataoff;
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file->f_version = 0;
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}
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return dataoff;
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}
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/*
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* ext4_seek_hole() retrieves the offset for SEEK_HOLE.
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*/
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static loff_t ext4_seek_hole(struct file *file, loff_t offset, loff_t maxsize)
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{
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struct inode *inode = file->f_mapping->host;
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struct ext4_map_blocks map;
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struct extent_status es;
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ext4_lblk_t start, last, end;
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loff_t holeoff, isize;
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int blkbits;
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int ret = 0;
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mutex_lock(&inode->i_mutex);
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isize = i_size_read(inode);
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if (offset >= isize) {
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mutex_unlock(&inode->i_mutex);
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return -ENXIO;
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}
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blkbits = inode->i_sb->s_blocksize_bits;
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start = offset >> blkbits;
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last = start;
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end = isize >> blkbits;
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holeoff = offset;
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do {
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map.m_lblk = last;
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map.m_len = end - last + 1;
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ret = ext4_map_blocks(NULL, inode, &map, 0);
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if (ret > 0 && !(map.m_flags & EXT4_MAP_UNWRITTEN)) {
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last += ret;
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holeoff = last << blkbits;
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continue;
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}
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/*
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* If there is a delay extent at this offset,
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* we will skip this extent.
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*/
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es.start = last;
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(void)ext4_es_find_extent(inode, &es);
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if (last >= es.start &&
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last < es.start + es.len) {
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last = es.start + es.len;
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holeoff = last << blkbits;
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continue;
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}
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/*
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* If there is a unwritten extent at this offset,
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* it will be as a data or a hole according to page
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* cache that has data or not.
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*/
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if (map.m_flags & EXT4_MAP_UNWRITTEN) {
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int unwritten;
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unwritten = ext4_find_unwritten_pgoff(inode, SEEK_HOLE,
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&map, &holeoff);
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if (!unwritten) {
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last += ret;
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holeoff = last << blkbits;
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continue;
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}
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}
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/* find a hole */
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break;
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} while (last <= end);
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mutex_unlock(&inode->i_mutex);
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if (holeoff > isize)
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holeoff = isize;
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if (holeoff < 0 && !(file->f_mode & FMODE_UNSIGNED_OFFSET))
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return -EINVAL;
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if (holeoff > maxsize)
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return -EINVAL;
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if (holeoff != file->f_pos) {
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file->f_pos = holeoff;
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file->f_version = 0;
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}
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return holeoff;
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}
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/*
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* ext4_llseek() handles both block-mapped and extent-mapped maxbytes values
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* by calling generic_file_llseek_size() with the appropriate maxbytes
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@ -300,8 +619,19 @@ loff_t ext4_llseek(struct file *file, loff_t offset, int origin)
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else
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maxbytes = inode->i_sb->s_maxbytes;
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return generic_file_llseek_size(file, offset, origin,
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maxbytes, i_size_read(inode));
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switch (origin) {
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case SEEK_SET:
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case SEEK_CUR:
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case SEEK_END:
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return generic_file_llseek_size(file, offset, origin,
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maxbytes, i_size_read(inode));
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case SEEK_DATA:
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return ext4_seek_data(file, offset, maxbytes);
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case SEEK_HOLE:
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return ext4_seek_hole(file, offset, maxbytes);
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}
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return -EINVAL;
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}
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const struct file_operations ext4_file_operations = {
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