[PATCH] generic_file_sendpage

[Jan Blunck]

This is a generic sendpage() for regular files.

With generic_file_sendpage() it is possible to use sendfile() on file 
targets, instead of only sending data to sockets.

This implementation is basically an extension of Joern's original patch 
(http://marc.theaimsgroup.com/?l=linux-kernel&m=109455958522766&w=2) but 
is honoring signals. I also removed some unnecessary code: no IOVs, no AIO.

qemu-debian:/home/root/sendfile_file# time ./fastcp 100mb test
real    0m11.037s
user    0m0.010s
sys     0m7.600s

qemu-debian:/home/root/sendfile_file# time cp 100mb test
real    0m13.342s
user    0m0.400s
sys     0m9.080s

Comments please,
Jan

Signed-off-by: Jörn Engel <joern@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Jan Blunck <j.blunck@xxxxxxxxxxxxx>

 fs/ext2/file.c     |    1 
 fs/ext3/file.c     |    1 
 include/linux/fs.h |    2 
 mm/filemap.c       |  170 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 174 insertions(+)

Index: linux-2.6/include/linux/fs.h
===================================================================
--- linux-2.6.orig/include/linux/fs.h
+++ linux-2.6/include/linux/fs.h
@@ -1502,6 +1502,8 @@ extern ssize_t do_sync_write(struct file
 ssize_t generic_file_write_nolock(struct file *file, const struct iovec *iov,
 				unsigned long nr_segs, loff_t *ppos);
 extern ssize_t generic_file_sendfile(struct file *, loff_t *, size_t, read_actor_t, void *);
+extern ssize_t generic_file_sendpage(struct file *, struct page *, int, size_t,
+				     loff_t *, int);
 extern void do_generic_mapping_read(struct address_space *mapping,
 				    struct file_ra_state *, struct file *,
 				    loff_t *, read_descriptor_t *, read_actor_t);
Index: linux-2.6/mm/filemap.c
===================================================================
--- linux-2.6.orig/mm/filemap.c
+++ linux-2.6/mm/filemap.c
@@ -1086,6 +1086,27 @@ int file_send_actor(read_descriptor_t * 
 	return written;
 }
 
+/*
+ * Simple generic file sendpage. Just write a kernel buffer to the file.
+ */
+static ssize_t
+__generic_kernel_file_write(struct file *, const char *, size_t, loff_t *);
+
+ssize_t generic_file_sendpage(struct file *file, struct page *page,
+			      int offset, size_t size, loff_t *ppos, int more)
+{
+	ssize_t ret;
+	char *kaddr;
+
+	kaddr = kmap(page);
+	ret = __generic_kernel_file_write(file, kaddr + offset, size, ppos);
+	kunmap(page);
+
+	return ret;
+}
+
+EXPORT_SYMBOL(generic_file_sendpage);
+
 ssize_t generic_file_sendfile(struct file *in_file, loff_t *ppos,
 			 size_t count, read_actor_t actor, void *target)
 {
@@ -1715,6 +1736,19 @@ int remove_suid(struct dentry *dentry)
 }
 EXPORT_SYMBOL(remove_suid);
 
+static inline size_t
+filemap_copy_from_kernel(struct page *page, unsigned long offset,
+			 const char *buf, unsigned bytes)
+{
+	char *kaddr;
+
+	kaddr = kmap(page);
+	memcpy(kaddr + offset, buf, bytes);
+	kunmap(page);
+
+	return bytes;
+}
+
 size_t
 __filemap_copy_from_user_iovec(char *vaddr, 
 			const struct iovec *iov, size_t base, size_t bytes)
@@ -1862,6 +1896,142 @@ generic_file_direct_write(struct kiocb *
 }
 EXPORT_SYMBOL(generic_file_direct_write);
 
+/*
+ * TODO:
+ * This largely tries to copy generic_file_aio_write_nolock(), although it
+ * doesn't have to be nearly as generic.  A real cleanup should either
+ * merge this into generic_file_aio_write_nolock() as well or keep it special
+ * and remove as much code as possible.
+ *
+ * Check for pending signals here. Otherwise return -EINTR early.
+ *
+ * No iov, no kiocb. If you think this is a problem, use the source ;)
+ */
+static ssize_t
+__generic_kernel_file_write(struct file *file, const char *buf,
+			    size_t count, loff_t *ppos)
+{
+	struct address_space * mapping = file->f_mapping;
+	struct address_space_operations *a_ops = mapping->a_ops;
+	struct inode 	*inode = mapping->host;
+	long		status = 0;
+	loff_t		pos;
+	struct page	*page;
+	struct page	*cached_page = NULL;
+	const int	isblk = S_ISBLK(inode->i_mode);
+	ssize_t		written;
+	ssize_t		err;
+	size_t		bytes;
+	struct pagevec	lru_pvec;
+
+	/* There is no sane reason to use O_DIRECT */
+	BUG_ON(file->f_flags & O_DIRECT);
+
+	if (unlikely(signal_pending(current)))
+		return -EINTR;
+
+	if (unlikely(count < 0))
+		return -EINVAL;
+
+	down(&inode->i_sem);
+
+	pos = *ppos;
+	pagevec_init(&lru_pvec, 0);
+
+	/* We can write back this queue in page reclaim */
+	current->backing_dev_info = mapping->backing_dev_info;
+	written = 0;
+
+	err = generic_write_checks(file, &pos, &count, isblk);
+	if (err)
+		goto out;
+
+	if (count == 0)
+		goto out;
+
+	remove_suid(file->f_dentry);
+	inode_update_time(inode, 1);
+
+	do {
+		unsigned long index;
+		unsigned long offset;
+		size_t copied;
+
+		offset = (pos & (PAGE_CACHE_SIZE -1)); /* Within page */
+		index = pos >> PAGE_CACHE_SHIFT;
+		bytes = PAGE_CACHE_SIZE - offset;
+		if (bytes > count)
+			bytes = count;
+
+		page = __grab_cache_page(mapping,index,&cached_page,&lru_pvec);
+		if (!page) {
+			status = -ENOMEM;
+			break;
+		}
+
+		status = a_ops->prepare_write(file, page, offset, offset+bytes);
+		if (unlikely(status)) {
+			loff_t isize = i_size_read(inode);
+			/*
+			 * prepare_write() may have instantiated a few blocks
+			 * outside i_size.  Trim these off again.
+			 */
+			unlock_page(page);
+			page_cache_release(page);
+			if (pos + bytes > isize)
+				vmtruncate(inode, isize);
+			break;
+		}
+
+		copied = filemap_copy_from_kernel(page, offset, buf, bytes);
+
+		flush_dcache_page(page);
+		status = a_ops->commit_write(file, page, offset, offset+bytes);
+		if (likely(copied > 0)) {
+			if (!status)
+				status = copied;
+
+			if (status >= 0) {
+				written += status;
+				count -= status;
+				pos += status;
+				buf += status;
+			}
+		}
+		if (unlikely(copied != bytes))
+			if (status >= 0)
+				status = -EFAULT;
+		unlock_page(page);
+		mark_page_accessed(page);
+		page_cache_release(page);
+		if (status < 0)
+			break;
+		balance_dirty_pages_ratelimited(mapping);
+		cond_resched();
+	} while (count);
+	*ppos = pos;
+
+	if (cached_page)
+		page_cache_release(cached_page);
+
+	/*
+	 * For now, when the user asks for O_SYNC, we'll actually give O_DSYNC
+	 */
+	if (status >= 0) {
+		if ((file->f_flags & O_SYNC) || IS_SYNC(inode))
+			status = generic_osync_inode(inode, mapping,
+					OSYNC_METADATA|OSYNC_DATA);
+	}
+
+	err = written ? written : status;
+out:
+	pagevec_lru_add(&lru_pvec);
+	current->backing_dev_info = 0;
+
+	up(&inode->i_sem);
+	return err;
+}
+
 ssize_t
 generic_file_buffered_write(struct kiocb *iocb, const struct iovec *iov,
 		unsigned long nr_segs, loff_t pos, loff_t *ppos,
Index: linux-2.6/fs/ext2/file.c
===================================================================
--- linux-2.6.orig/fs/ext2/file.c
+++ linux-2.6/fs/ext2/file.c
@@ -53,6 +53,7 @@ struct file_operations ext2_file_operati
 	.readv		= generic_file_readv,
 	.writev		= generic_file_writev,
 	.sendfile	= generic_file_sendfile,
+	.sendpage	= generic_file_sendpage,
 };
 
 #ifdef CONFIG_EXT2_FS_XIP
Index: linux-2.6/fs/ext3/file.c
===================================================================
--- linux-2.6.orig/fs/ext3/file.c
+++ linux-2.6/fs/ext3/file.c
@@ -119,6 +119,7 @@ struct file_operations ext3_file_operati
 	.release	= ext3_release_file,
 	.fsync		= ext3_sync_file,
 	.sendfile	= generic_file_sendfile,
+	.sendpage	= generic_file_sendpage,
 };
 
 struct inode_operations ext3_file_inode_operations = {