[PATCH 4/4] ext4: Switch to iomap for SEEK_HOLE / SEEK_DATA

Andreas Gruenbacher
2017-08-29T14:29:59Z

From: Christoph Hellwig <hch@lst.de>

Switch to the iomap_seek_hole and iomap_seek_data helpers for
implementing lseek SEEK_HOLE / SEEK_DATA, and remove all the code that
isn't needed any more.

Note that with this patch, ext4 will now always depend on the iomap code
instead of only when CONFIG_DAX is enabled, and it requires adding a
call into the extent status tree for iomap_begin as well to properly
deal with delalloc extents.

Signed-off-by: Christoph Hellwig <hch@lst.de>
[Minor fixes and cleanups by Andreas]
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
---
fs/ext4/Kconfig | 1 +
fs/ext4/ext4.h | 3 -
fs/ext4/file.c | 271 +++-----------------------------------------------------
fs/ext4/inode.c | 100 ++++++---------------
4 files changed, 43 insertions(+), 332 deletions(-)

diff --git a/fs/ext4/Kconfig b/fs/ext4/Kconfig
index e38039fd96ff..73b850f5659c 100644
--- a/fs/ext4/Kconfig
+++ b/fs/ext4/Kconfig
@@ -37,6 +37,7 @@ config EXT4_FS
select CRC16
select CRYPTO
select CRYPTO_CRC32C
+ select FS_IOMAP
help
This is the next generation of the ext3 filesystem.

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 017e55942a49..f295fce7a9c8 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -2515,9 +2515,6 @@ extern void ext4_da_update_reserve_space(struct inode *inode,
int used, int quota_claim);
extern int ext4_issue_zeroout(struct inode *inode, ext4_lblk_t lblk,
ext4_fsblk_t pblk, ext4_lblk_t len);
-extern int ext4_get_next_extent(struct inode *inode, ext4_lblk_t lblk,
- unsigned int map_len,
- struct extent_status *result);

/* indirect.c */
extern int ext4_ind_map_blocks(handle_t *handle, struct inode *inode,
diff --git a/fs/ext4/file.c b/fs/ext4/file.c
index 0d7cf0cc9b87..bc7a901c8b3f 100644
--- a/fs/ext4/file.c
+++ b/fs/ext4/file.c
@@ -20,6 +20,7 @@

#include <linux/time.h>
#include <linux/fs.h>
+#include <linux/iomap.h>
#include <linux/mount.h>
#include <linux/path.h>
#include <linux/dax.h>
@@ -455,256 +456,6 @@ 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 whence,
- ext4_lblk_t end_blk,
- 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 = (loff_t)end_blk << blkbits;
-
- index = startoff >> PAGE_SHIFT;
- end = (endoff - 1) >> PAGE_SHIFT;
-
- pagevec_init(&pvec, 0);
- do {
- int i, num;
- unsigned long nr_pages;
-
- num = min_t(pgoff_t, end - index, PAGEVEC_SIZE - 1) + 1;
- nr_pages = pagevec_lookup(&pvec, inode->i_mapping, index,
- (pgoff_t)num);
- if (nr_pages == 0)
- break;
-
- for (i = 0; i < nr_pages; i++) {
- struct page *page = pvec.pages[i];
- struct buffer_head *bh, *head;
-
- /*
- * If current offset is smaller than the page offset,
- * there is a hole at this offset.
- */
- if (whence == SEEK_HOLE && lastoff < endoff &&
- lastoff < page_offset(pvec.pages[i])) {
- found = 1;
- *offset = lastoff;
- goto out;
- }
-
- if (page->index > end)
- 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 (lastoff + bh->b_size <= startoff)
- goto next;
- if (buffer_uptodate(bh) ||
- buffer_unwritten(bh)) {
- if (whence == SEEK_DATA)
- found = 1;
- } else {
- if (whence == SEEK_HOLE)
- found = 1;
- }
- if (found) {
- *offset = max_t(loff_t,
- startoff, lastoff);
- unlock_page(page);
- goto out;
- }
-next:
- 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, we are done. */
- if (nr_pages < num)
- break;
-
- index = pvec.pages[i - 1]->index + 1;
- pagevec_release(&pvec);
- } while (index <= end);
-
- if (whence == SEEK_HOLE && lastoff < endoff) {
- found = 1;
- *offset = lastoff;
- }
-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 extent_status es;
- ext4_lblk_t start, last, end;
- loff_t dataoff, isize;
- int blkbits;
- int ret;
-
- inode_lock(inode);
-
- isize = i_size_read(inode);
- if (offset >= isize) {
- inode_unlock(inode);
- return -ENXIO;
- }
-
- blkbits = inode->i_sb->s_blocksize_bits;
- start = offset >> blkbits;
- last = start;
- end = isize >> blkbits;
- dataoff = offset;
-
- do {
- ret = ext4_get_next_extent(inode, last, end - last + 1, &es);
- if (ret <= 0) {
- /* No extent found -> no data */
- if (ret == 0)
- ret = -ENXIO;
- inode_unlock(inode);
- return ret;
- }
-
- last = es.es_lblk;
- if (last != start)
- dataoff = (loff_t)last << blkbits;
- if (!ext4_es_is_unwritten(&es))
- 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 (ext4_find_unwritten_pgoff(inode, SEEK_DATA,
- es.es_lblk + es.es_len, &dataoff))
- break;
- last += es.es_len;
- dataoff = (loff_t)last << blkbits;
- cond_resched();
- } while (last <= end);
-
- inode_unlock(inode);
-
- if (dataoff > isize)
- return -ENXIO;
-
- return vfs_setpos(file, dataoff, maxsize);
-}
-
-/*
- * 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 extent_status es;
- ext4_lblk_t start, last, end;
- loff_t holeoff, isize;
- int blkbits;
- int ret;
-
- inode_lock(inode);
-
- isize = i_size_read(inode);
- if (offset >= isize) {
- inode_unlock(inode);
- return -ENXIO;
- }
-
- blkbits = inode->i_sb->s_blocksize_bits;
- start = offset >> blkbits;
- last = start;
- end = isize >> blkbits;
- holeoff = offset;
-
- do {
- ret = ext4_get_next_extent(inode, last, end - last + 1, &es);
- if (ret < 0) {
- inode_unlock(inode);
- return ret;
- }
- /* Found a hole? */
- if (ret == 0 || es.es_lblk > last) {
- if (last != start)
- holeoff = (loff_t)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 (ext4_es_is_unwritten(&es) &&
- ext4_find_unwritten_pgoff(inode, SEEK_HOLE,
- last + es.es_len, &holeoff))
- break;
-
- last += es.es_len;
- holeoff = (loff_t)last << blkbits;
- cond_resched();
- } while (last <= end);
-
- inode_unlock(inode);
-
- if (holeoff > isize)
- holeoff = isize;
-
- return vfs_setpos(file, holeoff, maxsize);
-}
-
-/*
* ext4_llseek() handles both block-mapped and extent-mapped maxbytes values
* by calling generic_file_llseek_size() with the appropriate maxbytes
* value for each.
@@ -720,18 +471,24 @@ loff_t ext4_llseek(struct file *file, loff_t offset, int whence)
maxbytes = inode->i_sb->s_maxbytes;

switch (whence) {
- case SEEK_SET:
- case SEEK_CUR:
- case SEEK_END:
+ default:
return generic_file_llseek_size(file, offset, whence,
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);
+ inode_lock_shared(inode);
+ offset = iomap_seek_hole(inode, offset, &ext4_iomap_ops);
+ inode_unlock_shared(inode);
+ break;
+ case SEEK_DATA:
+ inode_lock_shared(inode);
+ offset = iomap_seek_data(inode, offset, &ext4_iomap_ops);
+ inode_unlock_shared(inode);
+ break;
}

- return -EINVAL;
+ if (offset < 0)
+ return offset;
+ return vfs_setpos(file, offset, maxbytes);
}

const struct file_operations ext4_file_operations = {
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index ab6ab835255e..f5895ea6ac70 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3400,7 +3400,6 @@ static int ext4_releasepage(struct page *page, gfp_t wait)
return try_to_free_buffers(page);
}

-#ifdef CONFIG_FS_DAX
static int ext4_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
unsigned flags, struct iomap *iomap)
{
@@ -3409,6 +3408,7 @@ static int ext4_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
unsigned long first_block = offset >> blkbits;
unsigned long last_block = (offset + length - 1) >> blkbits;
struct ext4_map_blocks map;
+ bool delalloc = false;
int ret;

if ((flags & IOMAP_REPORT) && ext4_has_inline_data(inode)) {
@@ -3425,6 +3425,29 @@ static int ext4_iomap_begin(struct inode *inode, loff_t offset, loff_t length,

if (!(flags & IOMAP_WRITE)) {
ret = ext4_map_blocks(NULL, inode, &map, 0);
+ if (ret < 0)
+ return ret;
+ if (!ret) {
+ struct extent_status es = {};
+
+ ext4_es_find_delayed_extent_range(inode, map.m_lblk,
+ map.m_lblk + map.m_len - 1, &es);
+ /* Is delalloc data before next block in extent tree? */
+ if (es.es_len && es.es_lblk < map.m_lblk + map.m_len) {
+ ext4_lblk_t offs = 0;
+
+ if (es.es_lblk < map.m_lblk)
+ offs = map.m_lblk - es.es_lblk;
+ map.m_lblk = es.es_lblk + offs;
+ map.m_pblk = ext4_es_pblock(&es) + offs;
+ map.m_len = es.es_len - offs;
+ if (ext4_es_is_unwritten(&es))
+ map.m_flags |= EXT4_MAP_UNWRITTEN;
+ if (ext4_es_is_delayed(&es))
+ delalloc = true;
+ ret = 1;
+ }
+ }
} else {
int dio_credits;
handle_t *handle;
@@ -3486,11 +3509,14 @@ static int ext4_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
else
iomap->dax_dev = NULL;
iomap->offset = first_block << blkbits;
+ iomap->length = (u64)map.m_len << blkbits;

if (ret == 0) {
iomap->type = IOMAP_HOLE;
iomap->addr = IOMAP_NULL_ADDR;
- iomap->length = (u64)map.m_len << blkbits;
+ } else if (delalloc) {
+ iomap->type = IOMAP_DELALLOC;
+ iomap->addr = IOMAP_NULL_ADDR;
} else {
if (map.m_flags & EXT4_MAP_MAPPED) {
iomap->type = IOMAP_MAPPED;
@@ -3501,7 +3527,6 @@ static int ext4_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
return -EIO;
}
iomap->addr = (u64)map.m_pblk << blkbits;
- iomap->length = (u64)map.m_len << blkbits;
}

if (map.m_flags & EXT4_MAP_NEW)
@@ -3567,8 +3592,6 @@ const struct iomap_ops ext4_iomap_ops = {
.iomap_end = ext4_iomap_end,
};

-#endif
-
static int ext4_end_io_dio(struct kiocb *iocb, loff_t offset,
ssize_t size, void *private)
{
@@ -6132,70 +6155,3 @@ int ext4_filemap_fault(struct vm_fault *vmf)

return err;
}
-
-/*
- * Find the first extent at or after @lblk in an inode that is not a hole.
- * Search for @map_len blocks at most. The extent is returned in @result.
- *
- * The function returns 1 if we found an extent. The function returns 0 in
- * case there is no extent at or after @lblk and in that case also sets
- * @result->es_len to 0. In case of error, the error code is returned.
- */
-int ext4_get_next_extent(struct inode *inode, ext4_lblk_t lblk,
- unsigned int map_len, struct extent_status *result)
-{
- struct ext4_map_blocks map;
- struct extent_status es = {};
- int ret;
-
- map.m_lblk = lblk;
- map.m_len = map_len;
-
- /*
- * For non-extent based files this loop may iterate several times since
- * we do not determine full hole size.
- */
- while (map.m_len > 0) {
- ret = ext4_map_blocks(NULL, inode, &map, 0);
- if (ret < 0)
- return ret;
- /* There's extent covering m_lblk? Just return it. */
- if (ret > 0) {
- int status;
-
- ext4_es_store_pblock(result, map.m_pblk);
- result->es_lblk = map.m_lblk;
- result->es_len = map.m_len;
- if (map.m_flags & EXT4_MAP_UNWRITTEN)
- status = EXTENT_STATUS_UNWRITTEN;
- else
- status = EXTENT_STATUS_WRITTEN;
- ext4_es_store_status(result, status);
- return 1;
- }
- ext4_es_find_delayed_extent_range(inode, map.m_lblk,
- map.m_lblk + map.m_len - 1,
- &es);
- /* Is delalloc data before next block in extent tree? */
- if (es.es_len && es.es_lblk < map.m_lblk + map.m_len) {
- ext4_lblk_t offset = 0;
-
- if (es.es_lblk < lblk)
- offset = lblk - es.es_lblk;
- result->es_lblk = es.es_lblk + offset;
- ext4_es_store_pblock(result,
- ext4_es_pblock(&es) + offset);
- result->es_len = es.es_len - offset;
- ext4_es_store_status(result, ext4_es_status(&es));
-
- return 1;
- }
- /* There's a hole at m_lblk, advance us after it */
- map.m_lblk += map.m_len;
- map_len -= map.m_len;
- map.m_len = map_len;
- cond_resched();
- }
- result->es_len = 0;
- return 0;
-}
--
2.13.3