ext4: Split uninitialized extents for direct I/O

When writing into an unitialized extent via direct I/O, and the direct
I/O doesn't exactly cover the unitialized extent, split the extent
into uninitialized and initialized extents before submitting the I/O.
This avoids needing to deal with an ENOSPC error in the end_io
callback that gets used for direct I/O.

When the IO is complete, the written extent will be marked as initialized.

Singed-Off-By: Mingming Cao <cmm@us.ibm.com> 
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

1 files changed, 386 insertions, 37 deletions

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index 7a3832577923..a38e651c004e 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -723,7 +723,7 @@ err:
  * insert new index [@logical;@ptr] into the block at @curp;
  * check where to insert: before @curp or after @curp
  */
-static int ext4_ext_insert_index(handle_t *handle, struct inode *inode,
+int ext4_ext_insert_index(handle_t *handle, struct inode *inode,
                                 struct ext4_ext_path *curp,
                                 int logical, ext4_fsblk_t ptr)
 {
@@ -1586,7 +1586,7 @@ out:
  */
 int ext4_ext_insert_extent(handle_t *handle, struct inode *inode,
                                 struct ext4_ext_path *path,
-                                struct ext4_extent *newext)
+                                struct ext4_extent *newext, int flag)
 {
         struct ext4_extent_header *eh;
         struct ext4_extent *ex, *fex;
@@ -1602,7 +1602,8 @@ int ext4_ext_insert_extent(handle_t *handle, struct inode *inode,
         BUG_ON(path[depth].p_hdr == NULL);
 
         /* try to insert block into found extent and return */
-        if (ex && ext4_can_extents_be_merged(inode, ex, newext)) {
+        if (ex && (flag != EXT4_GET_BLOCKS_DIO_CREATE_EXT)
+                && ext4_can_extents_be_merged(inode, ex, newext)) {
                 ext_debug("append [%d]%d block to %d:[%d]%d (from %llu)\n",
                                 ext4_ext_is_uninitialized(newext),
                                 ext4_ext_get_actual_len(newext),
@@ -1722,7 +1723,8 @@ has_space:
 
 merge:
         /* try to merge extents to the right */
-        ext4_ext_try_to_merge(inode, path, nearex);
+        if (flag != EXT4_GET_BLOCKS_DIO_CREATE_EXT)
+                ext4_ext_try_to_merge(inode, path, nearex);
 
         /* try to merge extents to the left */
 
@@ -2490,7 +2492,6 @@ static int ext4_ext_zeroout(struct inode *inode, struct ext4_extent *ex)
 }
 
 #define EXT4_EXT_ZERO_LEN 7
-
 /*
  * This function is called by ext4_ext_get_blocks() if someone tries to write
  * to an uninitialized extent. It may result in splitting the uninitialized
@@ -2583,7 +2584,8 @@ static int ext4_ext_convert_to_initialized(handle_t *handle,
                         ex3->ee_block = cpu_to_le32(iblock);
                         ext4_ext_store_pblock(ex3, newblock);
                         ex3->ee_len = cpu_to_le16(allocated);
-                        err = ext4_ext_insert_extent(handle, inode, path, ex3);
+                        err = ext4_ext_insert_extent(handle, inode, path,
+                                                        ex3, 0);
                         if (err == -ENOSPC) {
                                 err =  ext4_ext_zeroout(inode, &orig_ex);
                                 if (err)
@@ -2639,7 +2641,7 @@ static int ext4_ext_convert_to_initialized(handle_t *handle,
                 ext4_ext_store_pblock(ex3, newblock + max_blocks);
                 ex3->ee_len = cpu_to_le16(allocated - max_blocks);
                 ext4_ext_mark_uninitialized(ex3);
-                err = ext4_ext_insert_extent(handle, inode, path, ex3);
+                err = ext4_ext_insert_extent(handle, inode, path, ex3, 0);
                 if (err == -ENOSPC) {
                         err =  ext4_ext_zeroout(inode, &orig_ex);
                         if (err)
@@ -2757,7 +2759,7 @@ static int ext4_ext_convert_to_initialized(handle_t *handle,
         err = ext4_ext_dirty(handle, inode, path + depth);
         goto out;
 insert:
-        err = ext4_ext_insert_extent(handle, inode, path, &newex);
+        err = ext4_ext_insert_extent(handle, inode, path, &newex, 0);
         if (err == -ENOSPC) {
                 err =  ext4_ext_zeroout(inode, &orig_ex);
                 if (err)
@@ -2785,6 +2787,320 @@ fix_extent_len:
 }
 
 /*
+ * This function is called by ext4_ext_get_blocks() from
+ * ext4_get_blocks_dio_write() when DIO to write
+ * to an uninitialized extent.
+ *
+ * Writing to an uninitized extent may result in splitting the uninitialized
+ * extent into multiple /intialized unintialized extents (up to three)
+ * There are three possibilities:
+ *   a> There is no split required: Entire extent should be uninitialized
+ *   b> Splits in two extents: Write is happening at either end of the extent
+ *   c> Splits in three extents: Somone is writing in middle of the extent
+ *
+ * One of more index blocks maybe needed if the extent tree grow after
+ * the unintialized extent split. To prevent ENOSPC occur at the IO
+ * complete, we need to split the uninitialized extent before DIO submit
+ * the IO. The uninitilized extent called at this time will be split
+ * into three uninitialized extent(at most). After IO complete, the part
+ * being filled will be convert to initialized by the end_io callback function
+ * via ext4_convert_unwritten_extents().
+ */
+static int ext4_split_unwritten_extents(handle_t *handle,
+                                        struct inode *inode,
+                                        struct ext4_ext_path *path,
+                                        ext4_lblk_t iblock,
+                                        unsigned int max_blocks,
+                                        int flags)
+{
+        struct ext4_extent *ex, newex, orig_ex;
+        struct ext4_extent *ex1 = NULL;
+        struct ext4_extent *ex2 = NULL;
+        struct ext4_extent *ex3 = NULL;
+        struct ext4_extent_header *eh;
+        ext4_lblk_t ee_block;
+        unsigned int allocated, ee_len, depth;
+        ext4_fsblk_t newblock;
+        int err = 0;
+        int ret = 0;
+
+        ext_debug("ext4_split_unwritten_extents: inode %lu,"
+                  "iblock %llu, max_blocks %u\n", inode->i_ino,
+                  (unsigned long long)iblock, max_blocks);
+        depth = ext_depth(inode);
+        eh = path[depth].p_hdr;
+        ex = path[depth].p_ext;
+        ee_block = le32_to_cpu(ex->ee_block);
+        ee_len = ext4_ext_get_actual_len(ex);
+        allocated = ee_len - (iblock - ee_block);
+        newblock = iblock - ee_block + ext_pblock(ex);
+        ex2 = ex;
+        orig_ex.ee_block = ex->ee_block;
+        orig_ex.ee_len   = cpu_to_le16(ee_len);
+        ext4_ext_store_pblock(&orig_ex, ext_pblock(ex));
+
+        /*
+         * if the entire unintialized extent length less than
+         * the size of extent to write, there is no need to split
+         * uninitialized extent
+         */
+        if (allocated <= max_blocks)
+                return ret;
+
+        err = ext4_ext_get_access(handle, inode, path + depth);
+        if (err)
+                goto out;
+        /* ex1: ee_block to iblock - 1 : uninitialized */
+        if (iblock > ee_block) {
+                ex1 = ex;
+                ex1->ee_len = cpu_to_le16(iblock - ee_block);
+                ext4_ext_mark_uninitialized(ex1);
+                ex2 = &newex;
+        }
+        /*
+         * for sanity, update the length of the ex2 extent before
+         * we insert ex3, if ex1 is NULL. This is to avoid temporary
+         * overlap of blocks.
+         */
+        if (!ex1 && allocated > max_blocks)
+                ex2->ee_len = cpu_to_le16(max_blocks);
+        /* ex3: to ee_block + ee_len : uninitialised */
+        if (allocated > max_blocks) {
+                unsigned int newdepth;
+                ex3 = &newex;
+                ex3->ee_block = cpu_to_le32(iblock + max_blocks);
+                ext4_ext_store_pblock(ex3, newblock + max_blocks);
+                ex3->ee_len = cpu_to_le16(allocated - max_blocks);
+                ext4_ext_mark_uninitialized(ex3);
+                err = ext4_ext_insert_extent(handle, inode, path, ex3, flags);
+                if (err == -ENOSPC) {
+                        err =  ext4_ext_zeroout(inode, &orig_ex);
+                        if (err)
+                                goto fix_extent_len;
+                        /* update the extent length and mark as initialized */
+                        ex->ee_block = orig_ex.ee_block;
+                        ex->ee_len   = orig_ex.ee_len;
+                        ext4_ext_store_pblock(ex, ext_pblock(&orig_ex));
+                        ext4_ext_dirty(handle, inode, path + depth);
+                        /* zeroed the full extent */
+                        /* blocks available from iblock */
+                        return allocated;
+
+                } else if (err)
+                        goto fix_extent_len;
+                /*
+                 * The depth, and hence eh & ex might change
+                 * as part of the insert above.
+                 */
+                newdepth = ext_depth(inode);
+                /*
+                 * update the extent length after successful insert of the
+                 * split extent
+                 */
+                orig_ex.ee_len = cpu_to_le16(ee_len -
+                                                ext4_ext_get_actual_len(ex3));
+                depth = newdepth;
+                ext4_ext_drop_refs(path);
+                path = ext4_ext_find_extent(inode, iblock, path);
+                if (IS_ERR(path)) {
+                        err = PTR_ERR(path);
+                        goto out;
+                }
+                eh = path[depth].p_hdr;
+                ex = path[depth].p_ext;
+                if (ex2 != &newex)
+                        ex2 = ex;
+
+                err = ext4_ext_get_access(handle, inode, path + depth);
+                if (err)
+                        goto out;
+
+                allocated = max_blocks;
+        }
+        /*
+         * If there was a change of depth as part of the
+         * insertion of ex3 above, we need to update the length
+         * of the ex1 extent again here
+         */
+        if (ex1 && ex1 != ex) {
+                ex1 = ex;
+                ex1->ee_len = cpu_to_le16(iblock - ee_block);
+                ext4_ext_mark_uninitialized(ex1);
+                ex2 = &newex;
+        }
+        /*
+         * ex2: iblock to iblock + maxblocks-1 : to be direct IO written,
+         * uninitialised still.
+         */
+        ex2->ee_block = cpu_to_le32(iblock);
+        ext4_ext_store_pblock(ex2, newblock);
+        ex2->ee_len = cpu_to_le16(allocated);
+        ext4_ext_mark_uninitialized(ex2);
+        if (ex2 != ex)
+                goto insert;
+        /* Mark modified extent as dirty */
+        err = ext4_ext_dirty(handle, inode, path + depth);
+        ext_debug("out here\n");
+        goto out;
+insert:
+        err = ext4_ext_insert_extent(handle, inode, path, &newex, flags);
+        if (err == -ENOSPC) {
+                err =  ext4_ext_zeroout(inode, &orig_ex);
+                if (err)
+                        goto fix_extent_len;
+                /* update the extent length and mark as initialized */
+                ex->ee_block = orig_ex.ee_block;
+                ex->ee_len   = orig_ex.ee_len;
+                ext4_ext_store_pblock(ex, ext_pblock(&orig_ex));
+                ext4_ext_dirty(handle, inode, path + depth);
+                /* zero out the first half */
+                return allocated;
+        } else if (err)
+                goto fix_extent_len;
+out:
+        ext4_ext_show_leaf(inode, path);
+        return err ? err : allocated;
+
+fix_extent_len:
+        ex->ee_block = orig_ex.ee_block;
+        ex->ee_len   = orig_ex.ee_len;
+        ext4_ext_store_pblock(ex, ext_pblock(&orig_ex));
+        ext4_ext_mark_uninitialized(ex);
+        ext4_ext_dirty(handle, inode, path + depth);
+        return err;
+}
+static int ext4_convert_unwritten_extents_dio(handle_t *handle,
+                                              struct inode *inode,
+                                              struct ext4_ext_path *path)
+{
+        struct ext4_extent *ex;
+        struct ext4_extent_header *eh;
+        int depth;
+        int err = 0;
+        int ret = 0;
+
+        depth = ext_depth(inode);
+        eh = path[depth].p_hdr;
+        ex = path[depth].p_ext;
+
+        err = ext4_ext_get_access(handle, inode, path + depth);
+        if (err)
+                goto out;
+        /* first mark the extent as initialized */
+        ext4_ext_mark_initialized(ex);
+
+        /*
+         * We have to see if it can be merged with the extent
+         * on the left.
+         */
+        if (ex > EXT_FIRST_EXTENT(eh)) {
+                /*
+                 * To merge left, pass "ex - 1" to try_to_merge(),
+                 * since it merges towards right _only_.
+                 */
+                ret = ext4_ext_try_to_merge(inode, path, ex - 1);
+                if (ret) {
+                        err = ext4_ext_correct_indexes(handle, inode, path);
+                        if (err)
+                                goto out;
+                        depth = ext_depth(inode);
+                        ex--;
+                }
+        }
+        /*
+         * Try to Merge towards right.
+         */
+        ret = ext4_ext_try_to_merge(inode, path, ex);
+        if (ret) {
+                err = ext4_ext_correct_indexes(handle, inode, path);
+                if (err)
+                        goto out;
+                depth = ext_depth(inode);
+        }
+        /* Mark modified extent as dirty */
+        err = ext4_ext_dirty(handle, inode, path + depth);
+out:
+        ext4_ext_show_leaf(inode, path);
+        return err;
+}
+
+static int
+ext4_ext_handle_uninitialized_extents(handle_t *handle, struct inode *inode,
+                        ext4_lblk_t iblock, unsigned int max_blocks,
+                        struct ext4_ext_path *path, int flags,
+                        unsigned int allocated, struct buffer_head *bh_result,
+                        ext4_fsblk_t newblock)
+{
+        int ret = 0;
+        int err = 0;
+
+        ext_debug("ext4_ext_handle_uninitialized_extents: inode %lu, logical"
+                  "block %llu, max_blocks %u, flags %d, allocated %u",
+                  inode->i_ino, (unsigned long long)iblock, max_blocks,
+                  flags, allocated);
+        ext4_ext_show_leaf(inode, path);
+
+        /* DIO get_block() before submit the IO, split the extent */
+        if (flags == EXT4_GET_BLOCKS_DIO_CREATE_EXT) {
+                ret = ext4_split_unwritten_extents(handle,
+                                                inode, path, iblock,
+                                                max_blocks, flags);
+                goto out;
+        }
+        /* DIO end_io complete, convert the filled extent to written */
+        if (flags == EXT4_GET_BLOCKS_DIO_CONVERT_EXT) {
+                ret = ext4_convert_unwritten_extents_dio(handle, inode,
+                                                        path);
+                goto out2;
+        }
+        /* buffered IO case */
+        /*
+         * repeat fallocate creation request
+         * we already have an unwritten extent
+         */
+        if (flags & EXT4_GET_BLOCKS_UNINIT_EXT)
+                goto map_out;
+
+        /* buffered READ or buffered write_begin() lookup */
+        if ((flags & EXT4_GET_BLOCKS_CREATE) == 0) {
+                /*
+                 * We have blocks reserved already.  We
+                 * return allocated blocks so that delalloc
+                 * won't do block reservation for us.  But
+                 * the buffer head will be unmapped so that
+                 * a read from the block returns 0s.
+                 */
+                set_buffer_unwritten(bh_result);
+                goto out1;
+        }
+
+        /* buffered write, writepage time, convert*/
+        ret = ext4_ext_convert_to_initialized(handle, inode,
+                                                path, iblock,
+                                                max_blocks);
+out:
+        if (ret <= 0) {
+                err = ret;
+                goto out2;
+        } else
+                allocated = ret;
+        set_buffer_new(bh_result);
+map_out:
+        set_buffer_mapped(bh_result);
+out1:
+        if (allocated > max_blocks)
+                allocated = max_blocks;
+        ext4_ext_show_leaf(inode, path);
+        bh_result->b_bdev = inode->i_sb->s_bdev;
+        bh_result->b_blocknr = newblock;
+out2:
+        if (path) {
+                ext4_ext_drop_refs(path);
+                kfree(path);
+        }
+        return err ? err : allocated;
+}
+/*
  * Block allocation/map/preallocation routine for extents based files
  *
  *
@@ -2889,33 +3205,10 @@ int ext4_ext_get_blocks(handle_t *handle, struct inode *inode,
                                                         EXT4_EXT_CACHE_EXTENT);
                                 goto out;
                         }
-                        if (flags & EXT4_GET_BLOCKS_UNINIT_EXT)
-                                goto out;
-                        if ((flags & EXT4_GET_BLOCKS_CREATE) == 0) {
-                                if (allocated > max_blocks)
-                                        allocated = max_blocks;
-                                /*
-                                 * We have blocks reserved already.  We
-                                 * return allocated blocks so that delalloc
-                                 * won't do block reservation for us.  But
-                                 * the buffer head will be unmapped so that
-                                 * a read from the block returns 0s.
-                                 */
-                                set_buffer_unwritten(bh_result);
-                                bh_result->b_bdev = inode->i_sb->s_bdev;
-                                bh_result->b_blocknr = newblock;
-                                goto out2;
-                        }
-
-                        ret = ext4_ext_convert_to_initialized(handle, inode,
-                                                                path, iblock,
-                                                                max_blocks);
-                        if (ret <= 0) {
-                                err = ret;
-                                goto out2;
-                        } else
-                                allocated = ret;
-                        goto outnew;
+                        ret = ext4_ext_handle_uninitialized_extents(handle,
+                                        inode, iblock, max_blocks, path,
+                                        flags, allocated, bh_result, newblock);
+                        return ret;
                 }
         }
 
@@ -2988,7 +3281,7 @@ int ext4_ext_get_blocks(handle_t *handle, struct inode *inode,
         newex.ee_len = cpu_to_le16(ar.len);
         if (flags & EXT4_GET_BLOCKS_UNINIT_EXT)  /* Mark uninitialized */
                 ext4_ext_mark_uninitialized(&newex);
-        err = ext4_ext_insert_extent(handle, inode, path, &newex);
+        err = ext4_ext_insert_extent(handle, inode, path, &newex, flags);
         if (err) {
                 /* free data blocks we just allocated */
                 /* not a good idea to call discard here directly,
@@ -3002,7 +3295,6 @@ int ext4_ext_get_blocks(handle_t *handle, struct inode *inode,
         /* previous routine could use block we allocated */
         newblock = ext_pblock(&newex);
         allocated = ext4_ext_get_actual_len(&newex);
-outnew:
         set_buffer_new(bh_result);
 
         /* Cache only when it is _not_ an uninitialized extent */
@@ -3201,6 +3493,63 @@ retry:
 }
 
 /*
+ * This function convert a range of blocks to written extents
+ * The caller of this function will pass the start offset and the size.
+ * all unwritten extents within this range will be converted to
+ * written extents.
+ *
+ * This function is called from the direct IO end io call back
+ * function, to convert the fallocated extents after IO is completed.
+ */
+int ext4_convert_unwritten_extents(struct inode *inode, loff_t offset,
+                                    loff_t len)
+{
+        handle_t *handle;
+        ext4_lblk_t block;
+        unsigned int max_blocks;
+        int ret = 0;
+        int ret2 = 0;
+        struct buffer_head map_bh;
+        unsigned int credits, blkbits = inode->i_blkbits;
+
+        block = offset >> blkbits;
+        /*
+         * We can't just convert len to max_blocks because
+         * If blocksize = 4096 offset = 3072 and len = 2048
+         */
+        max_blocks = (EXT4_BLOCK_ALIGN(len + offset, blkbits) >> blkbits)
+                                                        - block;
+        /*
+         * credits to insert 1 extent into extent tree
+         */
+        credits = ext4_chunk_trans_blocks(inode, max_blocks);
+        while (ret >= 0 && ret < max_blocks) {
+                block = block + ret;
+                max_blocks = max_blocks - ret;
+                handle = ext4_journal_start(inode, credits);
+                if (IS_ERR(handle)) {
+                        ret = PTR_ERR(handle);
+                        break;
+                }
+                map_bh.b_state = 0;
+                ret = ext4_get_blocks(handle, inode, block,
+                                      max_blocks, &map_bh,
+                                      EXT4_GET_BLOCKS_DIO_CONVERT_EXT);
+                if (ret <= 0) {
+                        WARN_ON(ret <= 0);
+                        printk(KERN_ERR "%s: ext4_ext_get_blocks "
+                                    "returned error inode#%lu, block=%u, "
+                                    "max_blocks=%u", __func__,
+                                    inode->i_ino, block, max_blocks);
+                }
+                ext4_mark_inode_dirty(handle, inode);
+                ret2 = ext4_journal_stop(handle);
+                if (ret <= 0 || ret2 )
+                        break;
+        }
+        return ret > 0 ? ret2 : ret;
+}
+/*
  * Callback function called for each extent to gather FIEMAP information.
  */
 static int ext4_ext_fiemap_cb(struct inode *inode, struct ext4_ext_path *path,