vfs: allow custom EOF in generic_file_llseek code

For ext3/4 htree directories, using the vfs llseek function with
SEEK_END goes to i_size like for any other file, but in reality
we want the maximum possible hash value.  Recent changes
in ext4 have cut & pasted generic_file_llseek() back into fs/ext4/dir.c,
but replicating this core code seems like a bad idea, especially
since the copy has already diverged from the vfs.

This patch updates generic_file_llseek_size to accept
both a custom maximum offset, and a custom EOF position.  With this
in place, ext4_dir_llseek can pass in the appropriate maximum hash
position for both maxsize and eof, and get what it wants.

As far as I know, this does not fix any bugs - nfs in the kernel
doesn't use SEEK_END, and I don't know of any user who does.  But
some ext4 folks seem keen on doing the right thing here, and I can't
really argue.

(Patch also fixes up some comments slightly)

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

diff --git a/fs/ext3/dir.c b/fs/ext3/dir.c
index 92490e9f85ca0fc61a23f8142c0bb197758b1f1f..901f67e37864d5be4919e8816b9456444b73094d 100644 (file)
--- a/fs/ext3/dir.c
+++ b/fs/ext3/dir.c
@@ -303,7 +303,8 @@ loff_t ext3_dir_llseek(struct file *file, loff_t offset, int origin)
 
        if (likely(dx_dir))
                return generic_file_llseek_size(file, offset, origin,
-                                               ext3_get_htree_eof(file));
+                                               ext3_get_htree_eof(file),
+                                               i_size_read(inode));
        else
                return generic_file_llseek(file, offset, origin);
 }

diff --git a/fs/ext4/file.c b/fs/ext4/file.c
index 8c7642a00054fd1ddf649e733e4b6efb5a0eb14b..f3dadd0a0d51d0f6362d5397fa19bb68aebfcd70 100644 (file)
--- a/fs/ext4/file.c
+++ b/fs/ext4/file.c
@@ -225,7 +225,8 @@ loff_t ext4_llseek(struct file *file, loff_t offset, int origin)
        else
                maxbytes = inode->i_sb->s_maxbytes;
 
-       return generic_file_llseek_size(file, offset, origin, maxbytes);
+       return generic_file_llseek_size(file, offset, origin,
+                                       maxbytes, i_size_read(inode));
 }
 
 const struct file_operations ext4_file_operations = {

diff --git a/fs/read_write.c b/fs/read_write.c
index c20614f86c01ed88ed36a65e9dfafdabfd3ba4d3..1adfb691e4f152444d8b7a080c1159057bbed9ad 100644 (file)
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -55,10 +55,11 @@ static loff_t lseek_execute(struct file *file, struct inode *inode,
  * @file:      file structure to seek on
  * @offset:    file offset to seek to
  * @origin:    type of seek
- * @size:      max size of file system
+ * @size:      max size of this file in file system
+ * @eof:       offset used for SEEK_END position
  *
  * This is a variant of generic_file_llseek that allows passing in a custom
- * file size.
+ * maximum file size and a custom EOF position, for e.g. hashed directories
  *
  * Synchronization:
  * SEEK_SET and SEEK_END are unsynchronized (but atomic on 64bit platforms)
@@ -67,13 +68,13 @@ static loff_t lseek_execute(struct file *file, struct inode *inode,
  */
 loff_t
 generic_file_llseek_size(struct file *file, loff_t offset, int origin,
-               loff_t maxsize)
+               loff_t maxsize, loff_t eof)
 {
        struct inode *inode = file->f_mapping->host;
 
        switch (origin) {
        case SEEK_END:
-               offset += i_size_read(inode);
+               offset += eof;
                break;
        case SEEK_CUR:
                /*
@@ -99,7 +100,7 @@ generic_file_llseek_size(struct file *file, loff_t offset, int origin,
                 * In the generic case the entire file is data, so as long as
                 * offset isn't at the end of the file then the offset is data.
                 */
-               if (offset >= i_size_read(inode))
+               if (offset >= eof)
                        return -ENXIO;
                break;
        case SEEK_HOLE:
@@ -107,9 +108,9 @@ generic_file_llseek_size(struct file *file, loff_t offset, int origin,
                 * There is a virtual hole at the end of the file, so as long as
                 * offset isn't i_size or larger, return i_size.
                 */
-               if (offset >= i_size_read(inode))
+               if (offset >= eof)
                        return -ENXIO;
-               offset = i_size_read(inode);
+               offset = eof;
                break;
        }
 
@@ -132,7 +133,8 @@ loff_t generic_file_llseek(struct file *file, loff_t offset, int origin)
        struct inode *inode = file->f_mapping->host;
 
        return generic_file_llseek_size(file, offset, origin,
-                                       inode->i_sb->s_maxbytes);
+                                       inode->i_sb->s_maxbytes,
+                                       i_size_read(inode));
 }
 EXPORT_SYMBOL(generic_file_llseek);
 

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 6a6ca85bee238ffa35d732748fe2b62f334fa6fc..34acf51273dd6eb2655bf4cdf0f4c2747cb2de62 100644 (file)
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2454,7 +2454,7 @@ extern loff_t noop_llseek(struct file *file, loff_t offset, int origin);
 extern loff_t no_llseek(struct file *file, loff_t offset, int origin);
 extern loff_t generic_file_llseek(struct file *file, loff_t offset, int origin);
 extern loff_t generic_file_llseek_size(struct file *file, loff_t offset,
-               int origin, loff_t maxsize);
+               int origin, loff_t maxsize, loff_t eof);
 extern int generic_file_open(struct inode * inode, struct file * filp);
 extern int nonseekable_open(struct inode * inode, struct file * filp);