[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>

1 files changed, 28 insertions, 3 deletions

diff --git a/fs/fat/file.c b/fs/fat/file.c
index 15229fe569c..9b07c328a6f 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;
                 }
         }