ext4: Convert callers of ext4_get_blocks() to use ext4_map_blocks()

This saves a huge amount of stack space by avoiding unnecesary struct
buffer_head's from being allocated on the stack.

In addition, to make the code easier to understand, collapse and
refactor ext4_get_block(), ext4_get_block_write(),
noalloc_get_block_write(), into a single function.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

1 files changed, 127 insertions, 200 deletions

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index ff2f5fd681b..0b1d7c89f93 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -1336,133 +1336,112 @@ int ext4_map_blocks(handle_t *handle, struct inode *inode,
         return retval;
 }
 
-int ext4_get_blocks(handle_t *handle, struct inode *inode, sector_t block,
-                    unsigned int max_blocks, struct buffer_head *bh,
-                    int flags)
-{
-        struct ext4_map_blocks map;
-        int ret;
-
-        map.m_lblk = block;
-        map.m_len = max_blocks;
-
-        ret = ext4_map_blocks(handle, inode, &map, flags);
-        if (ret < 0)
-                return ret;
-
-        bh->b_blocknr = map.m_pblk;
-        bh->b_size = inode->i_sb->s_blocksize * map.m_len;
-        bh->b_bdev = inode->i_sb->s_bdev;
-        bh->b_state = (bh->b_state & ~EXT4_MAP_FLAGS) | map.m_flags;
-        return ret;
-}
-
 /* Maximum number of blocks we map for direct IO at once. */
 #define DIO_MAX_BLOCKS 4096
 
-int ext4_get_block(struct inode *inode, sector_t iblock,
-                   struct buffer_head *bh_result, int create)
+static int _ext4_get_block(struct inode *inode, sector_t iblock,
+                           struct buffer_head *bh, int flags)
 {
         handle_t *handle = ext4_journal_current_handle();
+        struct ext4_map_blocks map;
         int ret = 0, started = 0;
-        unsigned max_blocks = bh_result->b_size >> inode->i_blkbits;
         int dio_credits;
 
-        if (create && !handle) {
+        map.m_lblk = iblock;
+        map.m_len = bh->b_size >> inode->i_blkbits;
+
+        if (flags && !handle) {
                 /* Direct IO write... */
-                if (max_blocks > DIO_MAX_BLOCKS)
-                        max_blocks = DIO_MAX_BLOCKS;
-                dio_credits = ext4_chunk_trans_blocks(inode, max_blocks);
+                if (map.m_len > DIO_MAX_BLOCKS)
+                        map.m_len = DIO_MAX_BLOCKS;
+                dio_credits = ext4_chunk_trans_blocks(inode, map.m_len);
                 handle = ext4_journal_start(inode, dio_credits);
                 if (IS_ERR(handle)) {
                         ret = PTR_ERR(handle);
-                        goto out;
+                        return ret;
                 }
                 started = 1;
         }
 
-        ret = ext4_get_blocks(handle, inode, iblock, max_blocks, bh_result,
-                              create ? EXT4_GET_BLOCKS_CREATE : 0);
+        ret = ext4_map_blocks(handle, inode, &map, flags);
         if (ret > 0) {
-                bh_result->b_size = (ret << inode->i_blkbits);
+                map_bh(bh, inode->i_sb, map.m_pblk);
+                bh->b_state = (bh->b_state & ~EXT4_MAP_FLAGS) | map.m_flags;
+                bh->b_size = inode->i_sb->s_blocksize * map.m_len;
                 ret = 0;
         }
         if (started)
                 ext4_journal_stop(handle);
-out:
         return ret;
 }
 
+int ext4_get_block(struct inode *inode, sector_t iblock,
+                   struct buffer_head *bh, int create)
+{
+        return _ext4_get_block(inode, iblock, bh,
+                               create ? EXT4_GET_BLOCKS_CREATE : 0);
+}
+
 /*
  * `handle' can be NULL if create is zero
  */
 struct buffer_head *ext4_getblk(handle_t *handle, struct inode *inode,
                                 ext4_lblk_t block, int create, int *errp)
 {
-        struct buffer_head dummy;
+        struct ext4_map_blocks map;
+        struct buffer_head *bh;
         int fatal = 0, err;
-        int flags = 0;
 
         J_ASSERT(handle != NULL || create == 0);
 
-        dummy.b_state = 0;
-        dummy.b_blocknr = -1000;
-        buffer_trace_init(&dummy.b_history);
-        if (create)
-                flags |= EXT4_GET_BLOCKS_CREATE;
-        err = ext4_get_blocks(handle, inode, block, 1, &dummy, flags);
-        /*
-         * ext4_get_blocks() returns number of blocks mapped. 0 in
-         * case of a HOLE.
-         */
-        if (err > 0) {
-                if (err > 1)
-                        WARN_ON(1);
-                err = 0;
+        map.m_lblk = block;
+        map.m_len = 1;
+        err = ext4_map_blocks(handle, inode, &map,
+                              create ? EXT4_GET_BLOCKS_CREATE : 0);
+
+        if (err < 0)
+                *errp = err;
+        if (err <= 0)
+                return NULL;
+        *errp = 0;
+
+        bh = sb_getblk(inode->i_sb, map.m_pblk);
+        if (!bh) {
+                *errp = -EIO;
+                return NULL;
         }
-        *errp = err;
-        if (!err && buffer_mapped(&dummy)) {
-                struct buffer_head *bh;
-                bh = sb_getblk(inode->i_sb, dummy.b_blocknr);
-                if (!bh) {
-                        *errp = -EIO;
-                        goto err;
-                }
-                if (buffer_new(&dummy)) {
-                        J_ASSERT(create != 0);
-                        J_ASSERT(handle != NULL);
+        if (map.m_flags & EXT4_MAP_NEW) {
+                J_ASSERT(create != 0);
+                J_ASSERT(handle != NULL);
 
-                        /*
-                         * Now that we do not always journal data, we should
-                         * keep in mind whether this should always journal the
-                         * new buffer as metadata.  For now, regular file
-                         * writes use ext4_get_block instead, so it's not a
-                         * problem.
-                         */
-                        lock_buffer(bh);
-                        BUFFER_TRACE(bh, "call get_create_access");
-                        fatal = ext4_journal_get_create_access(handle, bh);
-                        if (!fatal && !buffer_uptodate(bh)) {
-                                memset(bh->b_data, 0, inode->i_sb->s_blocksize);
-                                set_buffer_uptodate(bh);
-                        }
-                        unlock_buffer(bh);
-                        BUFFER_TRACE(bh, "call ext4_handle_dirty_metadata");
-                        err = ext4_handle_dirty_metadata(handle, inode, bh);
-                        if (!fatal)
-                                fatal = err;
-                } else {
-                        BUFFER_TRACE(bh, "not a new buffer");
-                }
-                if (fatal) {
-                        *errp = fatal;
-                        brelse(bh);
-                        bh = NULL;
+                /*
+                 * Now that we do not always journal data, we should
+                 * keep in mind whether this should always journal the
+                 * new buffer as metadata.  For now, regular file
+                 * writes use ext4_get_block instead, so it's not a
+                 * problem.
+                 */
+                lock_buffer(bh);
+                BUFFER_TRACE(bh, "call get_create_access");
+                fatal = ext4_journal_get_create_access(handle, bh);
+                if (!fatal && !buffer_uptodate(bh)) {
+                        memset(bh->b_data, 0, inode->i_sb->s_blocksize);
+                        set_buffer_uptodate(bh);
                 }
-                return bh;
+                unlock_buffer(bh);
+                BUFFER_TRACE(bh, "call ext4_handle_dirty_metadata");
+                err = ext4_handle_dirty_metadata(handle, inode, bh);
+                if (!fatal)
+                        fatal = err;
+        } else {
+                BUFFER_TRACE(bh, "not a new buffer");
         }
-err:
-        return NULL;
+        if (fatal) {
+                *errp = fatal;
+                brelse(bh);
+                bh = NULL;
+        }
+        return bh;
 }
 
 struct buffer_head *ext4_bread(handle_t *handle, struct inode *inode,
@@ -2050,28 +2029,23 @@ static int mpage_da_submit_io(struct mpage_da_data *mpd)
 /*
  * mpage_put_bnr_to_bhs - walk blocks and assign them actual numbers
  *
- * @mpd->inode - inode to walk through
- * @exbh->b_blocknr - first block on a disk
- * @exbh->b_size - amount of space in bytes
- * @logical - first logical block to start assignment with
- *
  * the function goes through all passed space and put actual disk
  * block numbers into buffer heads, dropping BH_Delay and BH_Unwritten
  */
-static void mpage_put_bnr_to_bhs(struct mpage_da_data *mpd, sector_t logical,
-                                 struct buffer_head *exbh)
+static void mpage_put_bnr_to_bhs(struct mpage_da_data *mpd,
+                                 struct ext4_map_blocks *map)
 {
         struct inode *inode = mpd->inode;
         struct address_space *mapping = inode->i_mapping;
-        int blocks = exbh->b_size >> inode->i_blkbits;
-        sector_t pblock = exbh->b_blocknr, cur_logical;
+        int blocks = map->m_len;
+        sector_t pblock = map->m_pblk, cur_logical;
         struct buffer_head *head, *bh;
         pgoff_t index, end;
         struct pagevec pvec;
         int nr_pages, i;
 
-        index = logical >> (PAGE_CACHE_SHIFT - inode->i_blkbits);
-        end = (logical + blocks - 1) >> (PAGE_CACHE_SHIFT - inode->i_blkbits);
+        index = map->m_lblk >> (PAGE_CACHE_SHIFT - inode->i_blkbits);
+        end = (map->m_lblk + blocks - 1) >> (PAGE_CACHE_SHIFT - inode->i_blkbits);
         cur_logical = index << (PAGE_CACHE_SHIFT - inode->i_blkbits);
 
         pagevec_init(&pvec, 0);
@@ -2098,17 +2072,16 @@ static void mpage_put_bnr_to_bhs(struct mpage_da_data *mpd, sector_t logical,
 
                         /* skip blocks out of the range */
                         do {
-                                if (cur_logical >= logical)
+                                if (cur_logical >= map->m_lblk)
                                         break;
                                 cur_logical++;
                         } while ((bh = bh->b_this_page) != head);
 
                         do {
-                                if (cur_logical >= logical + blocks)
+                                if (cur_logical >= map->m_lblk + blocks)
                                         break;
 
-                                if (buffer_delay(bh) ||
-                                                buffer_unwritten(bh)) {
+                                if (buffer_delay(bh) || buffer_unwritten(bh)) {
 
                                         BUG_ON(bh->b_bdev != inode->i_sb->s_bdev);
 
@@ -2127,7 +2100,7 @@ static void mpage_put_bnr_to_bhs(struct mpage_da_data *mpd, sector_t logical,
                                 } else if (buffer_mapped(bh))
                                         BUG_ON(bh->b_blocknr != pblock);
 
-                                if (buffer_uninit(exbh))
+                                if (map->m_flags & EXT4_MAP_UNINIT)
                                         set_buffer_uninit(bh);
                                 cur_logical++;
                                 pblock++;
@@ -2138,21 +2111,6 @@ static void mpage_put_bnr_to_bhs(struct mpage_da_data *mpd, sector_t logical,
 }
 
 
-/*
- * __unmap_underlying_blocks - just a helper function to unmap
- * set of blocks described by @bh
- */
-static inline void __unmap_underlying_blocks(struct inode *inode,
-                                             struct buffer_head *bh)
-{
-        struct block_device *bdev = inode->i_sb->s_bdev;
-        int blocks, i;
-
-        blocks = bh->b_size >> inode->i_blkbits;
-        for (i = 0; i < blocks; i++)
-                unmap_underlying_metadata(bdev, bh->b_blocknr + i);
-}
-
 static void ext4_da_block_invalidatepages(struct mpage_da_data *mpd,
                                         sector_t logical, long blk_cnt)
 {
@@ -2214,7 +2172,7 @@ static void ext4_print_free_blocks(struct inode *inode)
 static int mpage_da_map_blocks(struct mpage_da_data *mpd)
 {
         int err, blks, get_blocks_flags;
-        struct buffer_head new;
+        struct ext4_map_blocks map;
         sector_t next = mpd->b_blocknr;
         unsigned max_blocks = mpd->b_size >> mpd->inode->i_blkbits;
         loff_t disksize = EXT4_I(mpd->inode)->i_disksize;
@@ -2255,15 +2213,15 @@ static int mpage_da_map_blocks(struct mpage_da_data *mpd)
          * EXT4_GET_BLOCKS_DELALLOC_RESERVE so the delalloc accounting
          * variables are updated after the blocks have been allocated.
          */
-        new.b_state = 0;
+        map.m_lblk = next;
+        map.m_len = max_blocks;
         get_blocks_flags = EXT4_GET_BLOCKS_CREATE;
         if (ext4_should_dioread_nolock(mpd->inode))
                 get_blocks_flags |= EXT4_GET_BLOCKS_IO_CREATE_EXT;
         if (mpd->b_state & (1 << BH_Delay))
                 get_blocks_flags |= EXT4_GET_BLOCKS_DELALLOC_RESERVE;
 
-        blks = ext4_get_blocks(handle, mpd->inode, next, max_blocks,
-                               &new, get_blocks_flags);
+        blks = ext4_map_blocks(handle, mpd->inode, &map, get_blocks_flags);
         if (blks < 0) {
                 err = blks;
                 /*
@@ -2305,10 +2263,13 @@ static int mpage_da_map_blocks(struct mpage_da_data *mpd)
         }
         BUG_ON(blks == 0);
 
-        new.b_size = (blks << mpd->inode->i_blkbits);
+        if (map.m_flags & EXT4_MAP_NEW) {
+                struct block_device *bdev = mpd->inode->i_sb->s_bdev;
+                int i;
 
-        if (buffer_new(&new))
-                __unmap_underlying_blocks(mpd->inode, &new);
+                for (i = 0; i < map.m_len; i++)
+                        unmap_underlying_metadata(bdev, map.m_pblk + i);
+        }
 
         /*
          * If blocks are delayed marked, we need to
@@ -2316,7 +2277,7 @@ static int mpage_da_map_blocks(struct mpage_da_data *mpd)
          */
         if ((mpd->b_state & (1 << BH_Delay)) ||
             (mpd->b_state & (1 << BH_Unwritten)))
-                mpage_put_bnr_to_bhs(mpd, next, &new);
+                mpage_put_bnr_to_bhs(mpd, &map);
 
         if (ext4_should_order_data(mpd->inode)) {
                 err = ext4_jbd2_file_inode(handle, mpd->inode);
@@ -2534,8 +2495,9 @@ static int __mpage_da_writepage(struct page *page,
  * initialized properly.
  */
 static int ext4_da_get_block_prep(struct inode *inode, sector_t iblock,
-                                  struct buffer_head *bh_result, int create)
+                                  struct buffer_head *bh, int create)
 {
+        struct ext4_map_blocks map;
         int ret = 0;
         sector_t invalid_block = ~((sector_t) 0xffff);
 
@@ -2543,16 +2505,22 @@ static int ext4_da_get_block_prep(struct inode *inode, sector_t iblock,
                 invalid_block = ~0;
 
         BUG_ON(create == 0);
-        BUG_ON(bh_result->b_size != inode->i_sb->s_blocksize);
+        BUG_ON(bh->b_size != inode->i_sb->s_blocksize);
+
+        map.m_lblk = iblock;
+        map.m_len = 1;
 
         /*
          * first, we need to know whether the block is allocated already
          * preallocated blocks are unmapped but should treated
          * the same as allocated blocks.
          */
-        ret = ext4_get_blocks(NULL, inode, iblock, 1,  bh_result, 0);
-        if ((ret == 0) && !buffer_delay(bh_result)) {
-                /* the block isn't (pre)allocated yet, let's reserve space */
+        ret = ext4_map_blocks(NULL, inode, &map, 0);
+        if (ret < 0)
+                return ret;
+        if (ret == 0) {
+                if (buffer_delay(bh))
+                        return 0; /* Not sure this could or should happen */
                 /*
                  * XXX: __block_prepare_write() unmaps passed block,
                  * is it OK?
@@ -2562,26 +2530,26 @@ static int ext4_da_get_block_prep(struct inode *inode, sector_t iblock,
                         /* not enough space to reserve */
                         return ret;
 
-                map_bh(bh_result, inode->i_sb, invalid_block);
-                set_buffer_new(bh_result);
-                set_buffer_delay(bh_result);
-        } else if (ret > 0) {
-                bh_result->b_size = (ret << inode->i_blkbits);
-                if (buffer_unwritten(bh_result)) {
-                        /* A delayed write to unwritten bh should
-                         * be marked new and mapped.  Mapped ensures
-                         * that we don't do get_block multiple times
-                         * when we write to the same offset and new
-                         * ensures that we do proper zero out for
-                         * partial write.
-                         */
-                        set_buffer_new(bh_result);
-                        set_buffer_mapped(bh_result);
-                }
-                ret = 0;
+                map_bh(bh, inode->i_sb, invalid_block);
+                set_buffer_new(bh);
+                set_buffer_delay(bh);
+                return 0;
         }
 
-        return ret;
+        map_bh(bh, inode->i_sb, map.m_pblk);
+        bh->b_state = (bh->b_state & ~EXT4_MAP_FLAGS) | map.m_flags;
+
+        if (buffer_unwritten(bh)) {
+                /* A delayed write to unwritten bh should be marked
+                 * new and mapped.  Mapped ensures that we don't do
+                 * get_block multiple times when we write to the same
+                 * offset and new ensures that we do proper zero out
+                 * for partial write.
+                 */
+                set_buffer_new(bh);
+                set_buffer_mapped(bh);
+        }
+        return 0;
 }
 
 /*
@@ -2603,21 +2571,8 @@ static int ext4_da_get_block_prep(struct inode *inode, sector_t iblock,
 static int noalloc_get_block_write(struct inode *inode, sector_t iblock,
                                    struct buffer_head *bh_result, int create)
 {
-        int ret = 0;
-        unsigned max_blocks = bh_result->b_size >> inode->i_blkbits;
-
         BUG_ON(bh_result->b_size != inode->i_sb->s_blocksize);
-
-        /*
-         * we don't want to do block allocation in writepage
-         * so call get_block_wrap with create = 0
-         */
-        ret = ext4_get_blocks(NULL, inode, iblock, max_blocks, bh_result, 0);
-        if (ret > 0) {
-                bh_result->b_size = (ret << inode->i_blkbits);
-                ret = 0;
-        }
-        return ret;
+        return _ext4_get_block(inode, iblock, bh_result, 0);
 }
 
 static int bget_one(handle_t *handle, struct buffer_head *bh)
@@ -3644,46 +3599,18 @@ out:
         return ret;
 }
 
+/*
+ * ext4_get_block used when preparing for a DIO write or buffer write.
+ * We allocate an uinitialized extent if blocks haven't been allocated.
+ * The extent will be converted to initialized after the IO is complete.
+ */
 static int ext4_get_block_write(struct inode *inode, sector_t iblock,
                    struct buffer_head *bh_result, int create)
 {
-        handle_t *handle = ext4_journal_current_handle();
-        int ret = 0;
-        unsigned max_blocks = bh_result->b_size >> inode->i_blkbits;
-        int dio_credits;
-        int started = 0;
-
         ext4_debug("ext4_get_block_write: inode %lu, create flag %d\n",
                    inode->i_ino, create);
-        /*
-         * ext4_get_block in prepare for a DIO write or buffer write.
-         * We allocate an uinitialized extent if blocks haven't been allocated.
-         * The extent will be converted to initialized after IO complete.
-         */
-        create = EXT4_GET_BLOCKS_IO_CREATE_EXT;
-
-        if (!handle) {
-                if (max_blocks > DIO_MAX_BLOCKS)
-                        max_blocks = DIO_MAX_BLOCKS;
-                dio_credits = ext4_chunk_trans_blocks(inode, max_blocks);
-                handle = ext4_journal_start(inode, dio_credits);
-                if (IS_ERR(handle)) {
-                        ret = PTR_ERR(handle);
-                        goto out;
-                }
-                started = 1;
-        }
-
-        ret = ext4_get_blocks(handle, inode, iblock, max_blocks, bh_result,
-                              create);
-        if (ret > 0) {
-                bh_result->b_size = (ret << inode->i_blkbits);
-                ret = 0;
-        }
-        if (started)
-                ext4_journal_stop(handle);
-out:
-        return ret;
+        return _ext4_get_block(inode, iblock, bh_result,
+                               EXT4_GET_BLOCKS_IO_CREATE_EXT);
 }
 
 static void dump_completed_IO(struct inode * inode)