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Date: Tue, 7 Jun 2011 18:07:42 +0300
From: amir73il@...rs.sourceforge.net
To: linux-ext4@...r.kernel.org
Cc: tytso@....edu, lczerner@...hat.com,
Amir Goldstein <amir73il@...rs.sf.net>,
Yongqiang Yang <xiaoqiangnk@...il.com>
Subject: [PATCH v1 15/36] 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 ++-
fs/ext4/snapshot.c | 269 ++++++++++++++++++++++++++++++++++++++++++++++++++++
fs/ext4/snapshot.h | 12 ++-
6 files changed, 346 insertions(+), 6 deletions(-)
diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 5564111..7d66f92 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -109,6 +109,8 @@ 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 */
@@ -1825,6 +1827,7 @@ 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 410bc8b..cdc1752 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);
@@ -1362,6 +1371,21 @@ 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,"
@@ -1371,7 +1395,7 @@ 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);
@@ -1430,7 +1454,7 @@ 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
@@ -1621,6 +1645,14 @@ 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 4ff3079..6e4d960 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 ebff8a1..91f5473 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;
diff --git a/fs/ext4/snapshot.c b/fs/ext4/snapshot.c
index ef84551..fc91ca4 100644
--- a/fs/ext4/snapshot.c
+++ b/fs/ext4/snapshot.c
@@ -59,3 +59,272 @@ int ext4_snapshot_map_blocks(handle_t *handle, struct inode *inode,
return err;
}
+/*
+ * COW helper functions
+ */
+
+/*
+ * copy buffer @bh to (locked) snapshot buffer @sbh and mark it uptodate
+ */
+static inline void
+__ext4_snapshot_copy_buffer(struct buffer_head *sbh,
+ struct buffer_head *bh)
+{
+ memcpy(sbh->b_data, bh->b_data, SNAPSHOT_BLOCK_SIZE);
+ set_buffer_uptodate(sbh);
+}
+
+/*
+ * ext4_snapshot_complete_cow()
+ * Unlock a newly COWed snapshot buffer and complete the COW operation.
+ * Optionally, sync the buffer to disk or add it to the current transaction
+ * as dirty data.
+ */
+static inline int
+ext4_snapshot_complete_cow(handle_t *handle, struct inode *snapshot,
+ struct buffer_head *sbh, struct buffer_head *bh, int sync)
+{
+ int err = 0;
+
+ unlock_buffer(sbh);
+ err = ext4_jbd2_file_inode(handle, snapshot);
+ if (err)
+ goto out;
+ mark_buffer_dirty(sbh);
+ if (sync)
+ sync_dirty_buffer(sbh);
+out:
+ return err;
+}
+
+/*
+ * ext4_snapshot_copy_buffer_cow()
+ * helper function for ext4_snapshot_test_and_cow()
+ * copy COWed buffer to new allocated (locked) snapshot buffer
+ * add complete the COW operation
+ */
+static inline int
+ext4_snapshot_copy_buffer_cow(handle_t *handle, struct inode *snapshot,
+ struct buffer_head *sbh,
+ struct buffer_head *bh)
+{
+ __ext4_snapshot_copy_buffer(sbh, bh);
+ return ext4_snapshot_complete_cow(handle, snapshot, sbh, bh, 0);
+}
+
+/*
+ * ext4_snapshot_copy_buffer()
+ * helper function for ext4_snapshot_take()
+ * used for initializing pre-allocated snapshot blocks
+ * copy buffer to snapshot buffer and sync to disk
+ * 'mask' block bitmap with exclude bitmap before copying to snapshot.
+ */
+void ext4_snapshot_copy_buffer(struct buffer_head *sbh,
+ struct buffer_head *bh, const char *mask)
+{
+ lock_buffer(sbh);
+ __ext4_snapshot_copy_buffer(sbh, bh);
+ unlock_buffer(sbh);
+ mark_buffer_dirty(sbh);
+ sync_dirty_buffer(sbh);
+}
+
+/*
+ * COW functions
+ */
+
+#ifdef CONFIG_EXT4_DEBUG
+static void
+__ext4_snapshot_trace_cow(const char *where, handle_t *handle,
+ struct super_block *sb, struct inode *inode,
+ struct buffer_head *bh, ext4_fsblk_t block,
+ int count, int cmd)
+{
+ unsigned long inode_group = 0;
+ ext4_grpblk_t inode_offset = 0;
+
+ if (inode) {
+ inode_group = (inode->i_ino - 1) /
+ EXT4_INODES_PER_GROUP(sb);
+ inode_offset = (inode->i_ino - 1) %
+ EXT4_INODES_PER_GROUP(sb);
+ }
+ snapshot_debug_hl(4, "%s(i:%d/%ld, b:%lld/%lld) "
+ "count=%d, h_ref=%d, cmd=%d\n",
+ where, inode_offset, inode_group,
+ SNAPSHOT_BLOCK_TUPLE(block),
+ count, handle->h_ref, cmd);
+}
+
+#define ext4_snapshot_trace_cow(where, handle, sb, inode, bh, blk, cnt, cmd) \
+ if (snapshot_enable_debug >= 4) \
+ __ext4_snapshot_trace_cow(where, handle, sb, inode, \
+ bh, block, count, cmd)
+#else
+#define ext4_snapshot_trace_cow(where, handle, sb, inode, bh, blk, cnt, cmd)
+#endif
+/*
+ * Begin COW or move operation.
+ * No locks needed here, because @handle is a per-task struct.
+ */
+static inline void ext4_snapshot_cow_begin(handle_t *handle)
+{
+ snapshot_debug_hl(4, "{\n");
+ handle->h_cowing = 1;
+}
+
+/*
+ * End COW or move operation.
+ * No locks needed here, because @handle is a per-task struct.
+ */
+static inline void ext4_snapshot_cow_end(const char *where,
+ handle_t *handle, ext4_fsblk_t block, int err)
+{
+ handle->h_cowing = 0;
+ snapshot_debug_hl(4, "} = %d\n", err);
+ snapshot_debug_hl(4, ".\n");
+ if (err < 0)
+ snapshot_debug(1, "%s(b:%lld/%lld) failed!"
+ " h_ref=%d, err=%d\n", where,
+ SNAPSHOT_BLOCK_TUPLE(block),
+ handle->h_ref, err);
+}
+
+/*
+ * ext4_snapshot_test_and_cow - COW metadata block
+ * @where: name of caller function
+ * @handle: JBD handle
+ * @inode: owner of blocks (NULL for global metadata blocks)
+ * @block: address of metadata block
+ * @bh: buffer head of metadata block
+ * @cow: if false, return 1 if block needs to be COWed
+ *
+ * Return values:
+ * = 1 - @block needs to be COWed
+ * = 0 - @block was COWed or doesn't need to be COWed
+ * < 0 - error
+ */
+int ext4_snapshot_test_and_cow(const char *where, handle_t *handle,
+ struct inode *inode, ext4_fsblk_t block,
+ struct buffer_head *bh, int cow)
+{
+ struct super_block *sb = handle->h_transaction->t_journal->j_private;
+ struct inode *active_snapshot = ext4_snapshot_has_active(sb);
+ struct buffer_head *sbh = NULL;
+ ext4_fsblk_t blk = 0;
+ int err = 0, clear = 0, count = 1;
+
+ if (!active_snapshot)
+ /* no active snapshot - no need to COW */
+ return 0;
+
+ ext4_snapshot_trace_cow(where, handle, sb, inode, bh, block, 1, cow);
+
+ if (IS_COWING(handle)) {
+ /* avoid recursion on active snapshot updates */
+ WARN_ON(inode && inode != active_snapshot);
+ snapshot_debug_hl(4, "active snapshot update - "
+ "skip block cow!\n");
+ return 0;
+ } else if (inode == active_snapshot) {
+ /* active snapshot may only be modified during COW */
+ snapshot_debug_hl(4, "active snapshot access denied!\n");
+ return -EPERM;
+ }
+
+ /* BEGIN COWing */
+ ext4_snapshot_cow_begin(handle);
+
+ if (inode)
+ clear = ext4_snapshot_excluded(inode);
+ if (clear < 0) {
+ /*
+ * excluded file block access - don't COW and
+ * mark block in exclude bitmap
+ */
+ snapshot_debug_hl(4, "file (%lu) excluded from snapshot - "
+ "mark block (%lld) in exclude bitmap\n",
+ inode->i_ino, block);
+ cow = 0;
+ }
+
+ if (clear < 0)
+ goto cowed;
+ if (!err) {
+ trace_cow_inc(handle, ok_bitmap);
+ goto cowed;
+ }
+
+ /* block is in use by snapshot - check if it is mapped */
+ err = ext4_snapshot_map_blocks(handle, active_snapshot, block, 1, &blk,
+ SNAPMAP_READ);
+ if (err < 0)
+ goto out;
+ if (err > 0) {
+ sbh = sb_find_get_block(sb, blk);
+ trace_cow_inc(handle, ok_mapped);
+ err = 0;
+ goto test_pending_cow;
+ }
+
+ /* block needs to be COWed */
+ err = 1;
+ if (!cow)
+ /* don't COW - we were just checking */
+ goto out;
+
+ err = -EIO;
+ /* make sure we hold an uptodate source buffer */
+ if (!bh || !buffer_mapped(bh))
+ goto out;
+ if (!buffer_uptodate(bh)) {
+ snapshot_debug(1, "warning: non uptodate buffer (%lld)"
+ " needs to be copied to active snapshot!\n",
+ block);
+ ll_rw_block(READ, 1, &bh);
+ wait_on_buffer(bh);
+ if (!buffer_uptodate(bh))
+ goto out;
+ }
+
+ /* try to allocate snapshot block to make a backup copy */
+ sbh = ext4_getblk(handle, active_snapshot, SNAPSHOT_IBLOCK(block),
+ SNAPMAP_COW, &err);
+ if (!sbh)
+ goto out;
+
+ blk = sbh->b_blocknr;
+ if (!err) {
+ /*
+ * we didn't allocate this block -
+ * another COWing task must have allocated it
+ */
+ trace_cow_inc(handle, ok_mapped);
+ goto test_pending_cow;
+ }
+
+ /*
+ * we allocated this block -
+ * copy block data to snapshot and complete COW operation
+ */
+ err = ext4_snapshot_copy_buffer_cow(handle, active_snapshot,
+ sbh, bh);
+ if (err)
+ goto out;
+ snapshot_debug(3, "block [%lld/%lld] of snapshot (%u) "
+ "mapped to block [%lld/%lld]\n",
+ SNAPSHOT_BLOCK_TUPLE(block),
+ active_snapshot->i_generation,
+ SNAPSHOT_BLOCK_TUPLE(sbh->b_blocknr));
+
+ trace_cow_inc(handle, copied);
+test_pending_cow:
+
+cowed:
+out:
+ brelse(sbh);
+ /* END COWing */
+ ext4_snapshot_cow_end(where, handle, block, err);
+ return err;
+}
+
diff --git a/fs/ext4/snapshot.h b/fs/ext4/snapshot.h
index ea87a5a..90cb33e 100644
--- a/fs/ext4/snapshot.h
+++ b/fs/ext4/snapshot.h
@@ -174,7 +174,17 @@ extern void ext4_snapshot_copy_buffer(struct buffer_head *sbh,
extern int ext4_snapshot_read_block_bitmap(struct super_block *sb,
unsigned int block_group, struct buffer_head *bitmap_bh);
-#define ext4_snapshot_cow(handle, inode, block, bh, cow) 0
+extern int ext4_snapshot_test_and_cow(const char *where,
+ handle_t *handle, struct inode *inode,
+ ext4_fsblk_t block, struct buffer_head *bh, int cow);
+
+/*
+ * test if a metadata block should be COWed
+ * and if it should, copy the block to the active snapshot
+ */
+#define ext4_snapshot_cow(handle, inode, block, bh, cow) \
+ ext4_snapshot_test_and_cow(__func__, handle, inode, \
+ block, bh, cow)
#define ext4_snapshot_move(handle, inode, block, pcount, move) (0)
--
1.7.4.1
--
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