Revert "ext4: remove no longer used functions in inode.c"

This reverts commit ccb4d7af914e0fe9b2f1022f8ea6c300463fd5e6.

This commit reintroduces functions ext4_block_truncate_page() and
ext4_block_zero_page_range() which has been previously removed in favour
of ext4_discard_partial_page_buffers().

In future commits we want to reintroduce those function and remove
ext4_discard_partial_page_buffers() since it is duplicating some code
and also partially duplicating work of truncate_pagecache_range(),
moreover the old implementation was much clearer.

Signed-off-by: Lukas Czerner <lczerner@redhat.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

2 files changed, 124 insertions, 0 deletions

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 5aae3d12d400..9f9719f08490 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -2096,6 +2096,10 @@ extern int ext4_alloc_da_blocks(struct inode *inode);
 extern void ext4_set_aops(struct inode *inode);
 extern int ext4_writepage_trans_blocks(struct inode *);
 extern int ext4_chunk_trans_blocks(struct inode *, int nrblocks);
+extern int ext4_block_truncate_page(handle_t *handle,
+                struct address_space *mapping, loff_t from);
+extern int ext4_block_zero_page_range(handle_t *handle,
+                struct address_space *mapping, loff_t from, loff_t length);
 extern int ext4_discard_partial_page_buffers(handle_t *handle,
                 struct address_space *mapping, loff_t from,
                 loff_t length, int flags);
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 11638d7982c9..9b3380327ae2 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3570,6 +3570,126 @@ next:
         return err;
 }
 
+/*
+ * ext4_block_truncate_page() zeroes out a mapping from file offset `from'
+ * up to the end of the block which corresponds to `from'.
+ * This required during truncate. We need to physically zero the tail end
+ * of that block so it doesn't yield old data if the file is later grown.
+ */
+int ext4_block_truncate_page(handle_t *handle,
+                struct address_space *mapping, loff_t from)
+{
+        unsigned offset = from & (PAGE_CACHE_SIZE-1);
+        unsigned length;
+        unsigned blocksize;
+        struct inode *inode = mapping->host;
+
+        blocksize = inode->i_sb->s_blocksize;
+        length = blocksize - (offset & (blocksize - 1));
+
+        return ext4_block_zero_page_range(handle, mapping, from, length);
+}
+
+/*
+ * ext4_block_zero_page_range() zeros out a mapping of length 'length'
+ * starting from file offset 'from'.  The range to be zero'd must
+ * be contained with in one block.  If the specified range exceeds
+ * the end of the block it will be shortened to end of the block
+ * that cooresponds to 'from'
+ */
+int ext4_block_zero_page_range(handle_t *handle,
+                struct address_space *mapping, loff_t from, loff_t length)
+{
+        ext4_fsblk_t index = from >> PAGE_CACHE_SHIFT;
+        unsigned offset = from & (PAGE_CACHE_SIZE-1);
+        unsigned blocksize, max, pos;
+        ext4_lblk_t iblock;
+        struct inode *inode = mapping->host;
+        struct buffer_head *bh;
+        struct page *page;
+        int err = 0;
+
+        page = find_or_create_page(mapping, from >> PAGE_CACHE_SHIFT,
+                                   mapping_gfp_mask(mapping) & ~__GFP_FS);
+        if (!page)
+                return -ENOMEM;
+
+        blocksize = inode->i_sb->s_blocksize;
+        max = blocksize - (offset & (blocksize - 1));
+
+        /*
+         * correct length if it does not fall between
+         * 'from' and the end of the block
+         */
+        if (length > max || length < 0)
+                length = max;
+
+        iblock = index << (PAGE_CACHE_SHIFT - inode->i_sb->s_blocksize_bits);
+
+        if (!page_has_buffers(page))
+                create_empty_buffers(page, blocksize, 0);
+
+        /* Find the buffer that contains "offset" */
+        bh = page_buffers(page);
+        pos = blocksize;
+        while (offset >= pos) {
+                bh = bh->b_this_page;
+                iblock++;
+                pos += blocksize;
+        }
+
+        err = 0;
+        if (buffer_freed(bh)) {
+                BUFFER_TRACE(bh, "freed: skip");
+                goto unlock;
+        }
+
+        if (!buffer_mapped(bh)) {
+                BUFFER_TRACE(bh, "unmapped");
+                ext4_get_block(inode, iblock, bh, 0);
+                /* unmapped? It's a hole - nothing to do */
+                if (!buffer_mapped(bh)) {
+                        BUFFER_TRACE(bh, "still unmapped");
+                        goto unlock;
+                }
+        }
+
+        /* Ok, it's mapped. Make sure it's up-to-date */
+        if (PageUptodate(page))
+                set_buffer_uptodate(bh);
+
+        if (!buffer_uptodate(bh)) {
+                err = -EIO;
+                ll_rw_block(READ, 1, &bh);
+                wait_on_buffer(bh);
+                /* Uhhuh. Read error. Complain and punt. */
+                if (!buffer_uptodate(bh))
+                        goto unlock;
+        }
+
+        if (ext4_should_journal_data(inode)) {
+                BUFFER_TRACE(bh, "get write access");
+                err = ext4_journal_get_write_access(handle, bh);
+                if (err)
+                        goto unlock;
+        }
+
+        zero_user(page, offset, length);
+
+        BUFFER_TRACE(bh, "zeroed end of block");
+
+        err = 0;
+        if (ext4_should_journal_data(inode)) {
+                err = ext4_handle_dirty_metadata(handle, inode, bh);
+        } else
+                mark_buffer_dirty(bh);
+
+unlock:
+        unlock_page(page);
+        page_cache_release(page);
+        return err;
+}
+
 int ext4_can_truncate(struct inode *inode)
 {
         if (S_ISREG(inode->i_mode))