From dce56fb8ceff9d052ebcebd21db9e070015142ab Mon Sep 17 00:00:00 2001
From: Simon Wilkinson <sxw@inf.ed.ac.uk>
Date: Mon, 26 Oct 2009 19:58:53 +0000
Subject: [PATCH] Fix prepare and commit_write to do the right thing

Even when we're doing syncronous writeback, as we currently do
for write() operations, it's important to correctly fill, and flag
the pages we're writing to. Not doing so has a huge performance
penalty, as it means even when we've just written a page, we have to
pull it back from the backing store for a read.

This code fixes prepare_write and commit_write (for RHEL5) and
write_begin and write_end (for Fedora) to correctly populate and
flag pages which are being written.

Change-Id: Iaa2165b9b429000dcf0c6dd452e3eb8033257277
Reviewed-on: http://gerrit.openafs.org/820
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>
---
 src/afs/LINUX/osi_vnodeops.c | 60 ++++++++++++++++++++++++++++++++++++++------
 1 file changed, 52 insertions(+), 8 deletions(-)

diff --git a/src/afs/LINUX/osi_vnodeops.c b/src/afs/LINUX/osi_vnodeops.c
index 1c5cd0a..52000a2 100644
--- a/src/afs/LINUX/osi_vnodeops.c
+++ b/src/afs/LINUX/osi_vnodeops.c
@@ -2227,15 +2227,23 @@ afs_linux_permission(struct inode *ip, int mode)
     return afs_convert_code(code);
 }
 
-#if !defined(HAVE_WRITE_BEGIN)
 static int
 afs_linux_commit_write(struct file *file, struct page *page, unsigned offset,
 		       unsigned to)
 {
     int code;
+    struct inode *inode = FILE_INODE(file);
+    loff_t pagebase = page_offset(page);
 
-    code = afs_linux_writepage_sync(file->f_dentry->d_inode, page,
-                                    offset, to - offset);
+    if (i_size_read(inode) < (pagebase + offset))
+	i_size_write(inode, pagebase + offset);
+
+    if (PageChecked(page)) {
+	SetPageUptodate(page);
+	ClearPageChecked(page);
+    }
+
+    code = afs_linux_writepage_sync(inode, page, offset, to - offset);
 
     return code;
 }
@@ -2244,20 +2252,47 @@ static int
 afs_linux_prepare_write(struct file *file, struct page *page, unsigned from,
 			unsigned to)
 {
+
+    /* http://kerneltrap.org/node/4941 details the expected behaviour of
+     * prepare_write. Essentially, if the page exists within the file,
+     * and is not being fully written, then we should populate it.
+     */
+
+    if (!PageUptodate(page)) {
+	loff_t pagebase = page_offset(page);
+	loff_t isize = i_size_read(page->mapping->host);
+
+	/* Is the location we are writing to beyond the end of the file? */
+	if (pagebase >= isize ||
+	    ((from == 0) && (pagebase + to) >= isize)) {
+	    zero_user_segments(page, 0, from, to, PAGE_CACHE_SIZE);
+	    SetPageChecked(page);
+	/* Are we we writing a full page */
+	} else if (from == 0 && to == PAGE_CACHE_SIZE) {
+	    SetPageChecked(page);
+	/* Is the page readable, if it's wronly, we don't care, because we're
+	 * not actually going to read from it ... */
+	} else if ((file->f_flags && O_ACCMODE) != O_WRONLY) {
+	    /* We don't care if fillpage fails, because if it does the page
+	     * won't be marked as up to date
+	     */
+	    afs_linux_fillpage(file, page);
+	}
+    }
     return 0;
 }
-#else
 
+#if defined(HAVE_WRITE_BEGIN)
 static int
 afs_linux_write_end(struct file *file, struct address_space *mapping,
                                 loff_t pos, unsigned len, unsigned copied,
                                 struct page *page, void *fsdata)
 {
     int code;
-    unsigned from = pos & (PAGE_CACHE_SIZE - 1);
+    unsigned int from = pos & (PAGE_CACHE_SIZE - 1);
+
+    code = afs_linux_commit_write(file, page, from, from + len);
 
-    code = afs_linux_writepage_sync(file->f_dentry->d_inode, page,
-                                    from, copied);
     unlock_page(page);
     page_cache_release(page);
     return code;
@@ -2270,10 +2305,19 @@ afs_linux_write_begin(struct file *file, struct address_space *mapping,
 {
     struct page *page;
     pgoff_t index = pos >> PAGE_CACHE_SHIFT;
+    unsigned int from = pos & (PAGE_CACHE_SIZE - 1);
+    int code;
+
     page = grab_cache_page_write_begin(mapping, index, flags);
     *pagep = page;
 
-    return 0;
+    code = afs_linux_prepare_write(file, page, from, from + len);
+    if (code) {
+	unlock_page(page);
+	page_cache_release(page);
+    }
+
+    return code;
 }
 #endif
 
-- 
1.9.4