Re: O_DIRECT fails in some kernel and FS

[Chris Mason <mason@suse.com>]

Ok, the tricky part of direct io on reiserfs is the tails.  But, 
since direct io isn't allowed on non-page aligned file sizes, we'll
never have direct io onto a normal file tail.

< 2.4.18 reiserfs versions allowed expanding truncates to set i_size
without creating the corresponding metadata, so we still have to deal
with that.  It means we could have a packed tail on any file size,
including those bigger than the 16k limit after which we don't create
tails any more.

Chris and I had initially decided to unpack the tails on file open
if O_DIRECT is used, but it seems cleaner to add a 
reiserfs_get_block_direct_io, and have it return -EINVAL if a read
went to a tail.  writes that happen to a tail will trigger tail
conversion.

Anyway, this patch is very lightly tested, I'll try all the corner
cases on sunday.

-chris

# against 2.4.18-pe7
#
--- temp.1/fs/reiserfs/inode.c Mon, 28 Jan 2002 09:51:50 -0500 
+++ temp.1(w)/fs/reiserfs/inode.c Sat, 02 Feb 2002 12:26:50 -0500 
@@ -445,6 +445,20 @@
     return reiserfs_get_block(inode, block, bh_result, GET_BLOCK_NO_HOLE) ;
 }
 
+static int reiserfs_get_block_direct_io (struct inode * inode, long block,
+			struct buffer_head * bh_result, int create) {
+    int ret ;
+
+    ret = reiserfs_get_block(inode, block, bh_result, create) ;
+
+    /* don't allow direct io onto tail pages */
+    if (ret == 0 && buffer_mapped(bh_result) && bh_result->b_blocknr == 0) {
+        ret = -EINVAL ;
+    }
+    return ret ;
+}
+
+
 /*
 ** helper function for when reiserfs_get_block is called for a hole
 ** but the file tail is still in a direct item
@@ -2050,11 +2064,20 @@
     return ret ;
 }
 
+static int reiserfs_direct_io(int rw, struct inode *inode, 
+                              struct kiobuf *iobuf, unsigned long blocknr,
+			      int blocksize) 
+{
+    return generic_direct_IO(rw, inode, iobuf, blocknr, blocksize,
+                             reiserfs_get_block_direct_io) ;
+}
+
 struct address_space_operations reiserfs_address_space_operations = {
     writepage: reiserfs_writepage,
     readpage: reiserfs_readpage, 
     sync_page: block_sync_page,
     prepare_write: reiserfs_prepare_write,
     commit_write: reiserfs_commit_write,
-    bmap: reiserfs_aop_bmap
+    bmap: reiserfs_aop_bmap,
+    direct_IO: reiserfs_direct_io,
 } ;