[PATCH] fat: support a truncate() for expanding size (generic_cont_expand)

This patch changes generic_cont_expand(), in order to share the code
with fatfs.

  - Use vmtruncate() if ->prepare_write() returns a error.

Even if ->prepare_write() returns an error, it may already have added some
blocks.  So, this truncates blocks outside of ->i_size by vmtruncate().

  - Add generic_cont_expand_simple().

The generic_cont_expand_simple() assumes that ->prepare_write() can handle
the block boundary.  With this, we don't need to care the extra byte.

And for expanding a file size by truncate(), fatfs uses the
added generic_cont_expand_simple().

Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

3 files changed, 76 insertions, 18 deletions

diff --git a/fs/buffer.c b/fs/buffer.c
index 5287be18633b..55023231e460 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -2160,11 +2160,12 @@ int block_read_full_page(struct page *page, get_block_t *get_block)
  * truncates.  Uses prepare/commit_write to allow the filesystem to
  * deal with the hole.  
  */
-int generic_cont_expand(struct inode *inode, loff_t size)
+static int __generic_cont_expand(struct inode *inode, loff_t size,
+                                 pgoff_t index, unsigned int offset)
 {
         struct address_space *mapping = inode->i_mapping;
         struct page *page;
-        unsigned long index, offset, limit;
+        unsigned long limit;
         int err;
 
         err = -EFBIG;
@@ -2176,24 +2177,24 @@ int generic_cont_expand(struct inode *inode, loff_t size)
         if (size > inode->i_sb->s_maxbytes)
                 goto out;
 
-        offset = (size & (PAGE_CACHE_SIZE-1)); /* Within page */
-
-        /* ugh.  in prepare/commit_write, if from==to==start of block, we 
-        ** skip the prepare.  make sure we never send an offset for the start
-        ** of a block
-        */
-        if ((offset & (inode->i_sb->s_blocksize - 1)) == 0) {
-                offset++;
-        }
-        index = size >> PAGE_CACHE_SHIFT;
         err = -ENOMEM;
         page = grab_cache_page(mapping, index);
         if (!page)
                 goto out;
         err = mapping->a_ops->prepare_write(NULL, page, offset, offset);
-        if (!err) {
-                err = mapping->a_ops->commit_write(NULL, page, offset, offset);
+        if (err) {
+                /*
+                 * ->prepare_write() may have instantiated a few blocks
+                 * outside i_size.  Trim these off again.
+                 */
+                unlock_page(page);
+                page_cache_release(page);
+                vmtruncate(inode, inode->i_size);
+                goto out;
         }
+
+        err = mapping->a_ops->commit_write(NULL, page, offset, offset);
+
         unlock_page(page);
         page_cache_release(page);
         if (err > 0)
@@ -2202,6 +2203,36 @@ out:
         return err;
 }
 
+int generic_cont_expand(struct inode *inode, loff_t size)
+{
+        pgoff_t index;
+        unsigned int offset;
+
+        offset = (size & (PAGE_CACHE_SIZE - 1)); /* Within page */
+
+        /* ugh.  in prepare/commit_write, if from==to==start of block, we
+        ** skip the prepare.  make sure we never send an offset for the start
+        ** of a block
+        */
+        if ((offset & (inode->i_sb->s_blocksize - 1)) == 0) {
+                /* caller must handle this extra byte. */
+                offset++;
+        }
+        index = size >> PAGE_CACHE_SHIFT;
+
+        return __generic_cont_expand(inode, size, index, offset);
+}
+
+int generic_cont_expand_simple(struct inode *inode, loff_t size)
+{
+        loff_t pos = size - 1;
+        pgoff_t index = pos >> PAGE_CACHE_SHIFT;
+        unsigned int offset = (pos & (PAGE_CACHE_SIZE - 1)) + 1;
+
+        /* prepare/commit_write can handle even if from==to==start of block. */
+        return __generic_cont_expand(inode, size, index, offset);
+}
+
 /*
  * For moronic filesystems that do not allow holes in file.
  * We may have to extend the file.
@@ -3145,6 +3176,7 @@ EXPORT_SYMBOL(fsync_bdev);
 EXPORT_SYMBOL(generic_block_bmap);
 EXPORT_SYMBOL(generic_commit_write);
 EXPORT_SYMBOL(generic_cont_expand);
+EXPORT_SYMBOL(generic_cont_expand_simple);
 EXPORT_SYMBOL(init_buffer);
 EXPORT_SYMBOL(invalidate_bdev);
 EXPORT_SYMBOL(ll_rw_block);
diff --git a/fs/fat/file.c b/fs/fat/file.c
index 15229fe569c3..9b07c328a6fc 100644
--- a/fs/fat/file.c
+++ b/fs/fat/file.c
@@ -11,6 +11,7 @@
 #include <linux/msdos_fs.h>
 #include <linux/smp_lock.h>
 #include <linux/buffer_head.h>
+#include <linux/writeback.h>
 
 int fat_generic_ioctl(struct inode *inode, struct file *filp,
                       unsigned int cmd, unsigned long arg)
@@ -124,6 +125,24 @@ struct file_operations fat_file_operations = {
         .sendfile       = generic_file_sendfile,
 };
 
+static int fat_cont_expand(struct inode *inode, loff_t size)
+{
+        struct address_space *mapping = inode->i_mapping;
+        loff_t start = inode->i_size, count = size - inode->i_size;
+        int err;
+
+        err = generic_cont_expand_simple(inode, size);
+        if (err)
+                goto out;
+
+        inode->i_ctime = inode->i_mtime = CURRENT_TIME_SEC;
+        mark_inode_dirty(inode);
+        if (IS_SYNC(inode))
+                err = sync_page_range_nolock(inode, mapping, start, count);
+out:
+        return err;
+}
+
 int fat_notify_change(struct dentry *dentry, struct iattr *attr)
 {
         struct msdos_sb_info *sbi = MSDOS_SB(dentry->d_sb);
@@ -132,11 +151,17 @@ int fat_notify_change(struct dentry *dentry, struct iattr *attr)
 
         lock_kernel();
 
-        /* FAT cannot truncate to a longer file */
+        /*
+         * Expand the file. Since inode_setattr() updates ->i_size
+         * before calling the ->truncate(), but FAT needs to fill the
+         * hole before it.
+         */
         if (attr->ia_valid & ATTR_SIZE) {
                 if (attr->ia_size > inode->i_size) {
-                        error = -EPERM;
-                        goto out;
+                        error = fat_cont_expand(inode, attr->ia_size);
+                        if (error || attr->ia_valid == ATTR_SIZE)
+                                goto out;
+                        attr->ia_valid &= ~ATTR_SIZE;
                 }
         }
 
diff --git a/include/linux/buffer_head.h b/include/linux/buffer_head.h
index 1db061bb6b08..9f159baf153f 100644
--- a/include/linux/buffer_head.h
+++ b/include/linux/buffer_head.h
@@ -197,7 +197,8 @@ int block_read_full_page(struct page*, get_block_t*);
 int block_prepare_write(struct page*, unsigned, unsigned, get_block_t*);
 int cont_prepare_write(struct page*, unsigned, unsigned, get_block_t*,
                                 loff_t *);
-int generic_cont_expand(struct inode *inode, loff_t size) ;
+int generic_cont_expand(struct inode *inode, loff_t size);
+int generic_cont_expand_simple(struct inode *inode, loff_t size);
 int block_commit_write(struct page *page, unsigned from, unsigned to);
 int block_sync_page(struct page *);
 sector_t generic_block_bmap(struct address_space *, sector_t, get_block_t *);