Hi Zheng,
On 10/26/2012 09:23 PM, Zheng Liu wrote:
From: Zheng Liu <wenqing.lz@xxxxxxxxxx>
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: "Theodore Ts'o" <tytso@xxxxxxx>
CC: Hugh Dickins <hughd@xxxxxxxxxx>
Signed-off-by: Jie Liu <jeff.liu@xxxxxxxxxx>
Signed-off-by: Zheng Liu <wenqing.lz@xxxxxxxxxx>
---
v3 <- v2:
- determine an unwritten extent as a data/hole according to the whether there
has some data in page cache or not.
- remove ext4_seek_data_hole(), and call ext4_seek_data/hole() directly.
- fix some bugs
Please apply this patch before testing this patch using xfstest #285 due to
there is a bug in xfstest (http://patchwork.xfs.org/patch/4276/).
The function ext4_find_unwritten_pgoff() is inspired by Jeff's work for xfs
(d126d43f631f996daeee5006714fed914be32368). Thus, I add a Signed-off-by for
his crediting.
Jeff, I really appreicate if you could allow me to add Signed-off-by in this
patch. Please let me know if you think it is not well. Thanks!
I'm fine. :)
Finally, maybe I'll try to tweak that routine with page cache lookup for
unwritten extents to be a
VFS helper so that Btrfs can make use of it as well, thank you!
-Jeff
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 bf3966b..2f5759e 100644
--- a/fs/ext4/file.c
+++ b/fs/ext4/file.c
@@ -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"
@@ -286,6 +287,324 @@ static int ext4_file_open(struct inode * inode, struct file * 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
* value for each.
@@ -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 = {
--
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