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Date: Mon, 9 May 2011 19:41:33 +0300
From: amir73il@...rs.sourceforge.net
To: linux-ext4@...r.kernel.org
Cc: tytso@....edu, Amir Goldstein <amir73il@...rs.sf.net>,
Yongqiang Yang <xiaoqiangnk@...il.com>
Subject: [PATCH RFC 15/30] ext4: snapshot block operation - copy blocks to snapshot
From: Amir Goldstein <amir73il@...rs.sf.net>
Implementation of copying blocks into a snapshot file.
This mechanism is used to copy-on-write metadata blocks to snapshot.
Signed-off-by: Amir Goldstein <amir73il@...rs.sf.net>
Signed-off-by: Yongqiang Yang <xiaoqiangnk@...il.com>
---
fs/ext4/ext4.h | 3 +++
fs/ext4/inode.c | 40 ++++++++++++++++++++++++++++++++++++----
fs/ext4/mballoc.c | 18 ++++++++++++++++++
fs/ext4/resize.c | 10 +++++++++-
4 files changed, 66 insertions(+), 5 deletions(-)
diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index c7fd33e..942cd9c 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -122,6 +122,8 @@ typedef unsigned int ext4_group_t;
/* We are doing stream allocation */
#define EXT4_MB_STREAM_ALLOC 0x0800
+/* allocate blocks for active snapshot */
+#define EXT4_MB_HINT_COWING 0x02000
struct ext4_allocation_request {
/* target inode for block we're allocating */
@@ -1836,6 +1838,7 @@ extern void __ext4_free_blocks(const char *where, unsigned int line,
extern int ext4_mb_add_groupinfo(struct super_block *sb,
ext4_group_t i, struct ext4_group_desc *desc);
extern int ext4_trim_fs(struct super_block *, struct fstrim_range *);
+extern int ext4_mb_test_bit_range(int bit, void *addr, int *pcount);
/* inode.c */
struct buffer_head *ext4_getblk(handle_t *, struct inode *,
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index ba66545..b930645 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -699,8 +699,17 @@ static int ext4_alloc_blocks(handle_t *handle, struct inode *inode,
ar.goal = goal;
ar.len = target;
ar.logical = iblock;
- if (S_ISREG(inode->i_mode))
- /* enable in-core preallocation only for regular files */
+ if (IS_COWING(handle)) {
+ /*
+ * This hint is used to tell the allocator not to fail
+ * on quota limits and allow allocation from blocks which
+ * are reserved for snapshots.
+ * Failing allocation during COW operations would result
+ * in I/O error, which is not desirable.
+ */
+ ar.flags = EXT4_MB_HINT_COWING;
+ } else if (S_ISREG(inode->i_mode) && !ext4_snapshot_file(inode))
+ /* Enable preallocation only for non-snapshot regular files */
ar.flags = EXT4_MB_HINT_DATA;
current_block = ext4_mb_new_blocks(handle, &ar, err);
@@ -1359,6 +1368,21 @@ int ext4_map_blocks(handle_t *handle, struct inode *inode,
struct ext4_map_blocks *map, int flags)
{
int retval;
+ int cowing = 0;
+
+ if (handle && IS_COWING(handle)) {
+ /*
+ * locking order for locks validator:
+ * inode (VFS operation) -> active snapshot (COW operation)
+ *
+ * The i_data_sem lock is nested during COW operation, but
+ * the active snapshot i_data_sem write lock is not taken
+ * otherwise, because snapshot file has read-only aops and
+ * because truncate/unlink of active snapshot is not permitted.
+ */
+ BUG_ON(!ext4_snapshot_is_active(inode));
+ cowing = 1;
+ }
map->m_flags = 0;
ext_debug("ext4_map_blocks(): inode %lu, flag %d, max_blocks %u,"
@@ -1368,7 +1392,7 @@ int ext4_map_blocks(handle_t *handle, struct inode *inode,
* Try to see if we can get the block without requesting a new
* file system block.
*/
- down_read((&EXT4_I(inode)->i_data_sem));
+ down_read_nested((&EXT4_I(inode)->i_data_sem), cowing);
if (ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)) {
retval = ext4_ext_map_blocks(handle, inode, map,
flags & EXT4_GET_BLOCKS_MOVE_ON_WRITE);
@@ -1427,7 +1451,7 @@ int ext4_map_blocks(handle_t *handle, struct inode *inode,
* the write lock of i_data_sem, and call get_blocks()
* with create == 1 flag.
*/
- down_write((&EXT4_I(inode)->i_data_sem));
+ down_write_nested((&EXT4_I(inode)->i_data_sem), cowing);
/*
* if the caller is from delayed allocation writeout path
@@ -1618,6 +1642,14 @@ struct buffer_head *ext4_getblk(handle_t *handle, struct inode *inode,
J_ASSERT(create != 0);
J_ASSERT(handle != NULL);
+ if (SNAPMAP_ISCOW(create)) {
+ /* COWing block or creating COW bitmap */
+ lock_buffer(bh);
+ clear_buffer_uptodate(bh);
+ /* flag locked buffer and return */
+ *errp = 1;
+ return bh;
+ }
/*
* Now that we do not always journal data, we should
* keep in mind whether this should always journal the
diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 5eced75..d43f493 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -420,6 +420,24 @@ static inline int mb_find_next_bit(void *addr, int max, int start)
return ret;
}
+/*
+ * Find the largest range of set or clear bits.
+ * Return 1 for set bits and 0 for clear bits.
+ * Set *pcount to number of bits in range.
+ */
+int ext4_mb_test_bit_range(int bit, void *addr, int *pcount)
+{
+ int i, ret;
+
+ ret = mb_test_bit(bit, addr);
+ if (ret)
+ i = mb_find_next_zero_bit(addr, bit + *pcount, bit);
+ else
+ i = mb_find_next_bit(addr, bit + *pcount, bit);
+ *pcount = i - bit;
+ return ret ? 1 : 0;
+}
+
static void *mb_find_buddy(struct ext4_buddy *e4b, int order, int *max)
{
char *bb;
diff --git a/fs/ext4/resize.c b/fs/ext4/resize.c
index ee9b999..06c11fd 100644
--- a/fs/ext4/resize.c
+++ b/fs/ext4/resize.c
@@ -673,7 +673,15 @@ static void update_backups(struct super_block *sb,
(err = ext4_journal_restart(handle, EXT4_MAX_TRANS_DATA)))
break;
- bh = sb_getblk(sb, group * bpg + blk_off);
+ if (ext4_snapshot_has_active(sb))
+ /*
+ * test_and_cow() expects an uptodate buffer.
+ * Read the buffer here to suppress the
+ * "non uptodate buffer" warning.
+ */
+ bh = sb_bread(sb, group * bpg + blk_off);
+ else
+ bh = sb_getblk(sb, group * bpg + blk_off);
if (!bh) {
err = -EIO;
break;
--
1.7.0.4
--
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