提交 c8c0df24 编写于 作者: Z Zheng Liu 提交者: Theodore Ts'o

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: NJie Liu <jeff.liu@oracle.com>
Signed-off-by: NZheng Liu <wenqing.lz@taobao.com>
Signed-off-by: N"Theodore Ts'o" <tytso@mit.edu>
上级 b3aff3e3
......@@ -24,6 +24,7 @@
#include <linux/mount.h>
#include <linux/path.h>
#include <linux/quotaops.h>
#include <linux/pagevec.h>
#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;
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 = {
......
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