[PATCH] tmpfs: add support for read_iter and write_iter

[Hugh Dickins <hughd@google.com>]

Convert tmpfs do_shmem_file_read() to shmem_file_read_iter().
Make file_read_iter_actor() global so tmpfs can use it too: delete
file_read_actor(), which was made global in 2.4.4 for use by tmpfs.
Replace tmpfs generic_file_aio_write() by generic_file_write_iter().

Signed-off-by: Hugh Dickins <hughd@google.com>
---
Please add this to the end of your loop O_DIRECT series.  I tested loop
on tmpfs successfully with .direct_IO = shmem_direct_IO() { return 0; }
but that's better left as a patch for separate discussion.

Hmm, I don't see an equivalent of the old fault_in_pages_writeable():
have I missed it, or is that a problem?

 include/linux/fs.h |    5 ++-
 mm/filemap.c       |   42 +----------------------------
 mm/shmem.c         |   61 +++++++++++++------------------------------
 3 files changed, 24 insertions(+), 84 deletions(-)

--- 3.8-dk/include/linux/fs.h	2013-01-29 14:40:40.272041622 -0800
+++ linux/include/linux/fs.h	2013-02-02 20:40:07.316296654 -0800
@@ -2458,8 +2458,9 @@ extern int sb_min_blocksize(struct super
 extern int generic_file_mmap(struct file *, struct vm_area_struct *);
 extern int generic_file_readonly_mmap(struct file *, struct vm_area_struct *);
 extern int generic_file_remap_pages(struct vm_area_struct *, unsigned long addr,
-		unsigned long size, pgoff_t pgoff);
-extern int file_read_actor(read_descriptor_t * desc, struct page *page, unsigned long offset, unsigned long size);
+				unsigned long size, pgoff_t pgoff);
+extern int file_read_iter_actor(read_descriptor_t *desc, struct page *page,
+				unsigned long offset, unsigned long size);
 int generic_write_checks(struct file *file, loff_t *pos, size_t *count, int isblk);
 extern ssize_t generic_file_aio_read(struct kiocb *, const struct iovec *, unsigned long, loff_t);
 extern ssize_t generic_file_read_iter(struct kiocb *, struct iov_iter *,
--- 3.8-dk/mm/filemap.c	2013-01-29 14:40:12.520040962 -0800
+++ linux/mm/filemap.c	2013-02-02 20:40:17.728296902 -0800
@@ -1295,44 +1295,6 @@ out:
 	file_accessed(filp);
 }
 
-int file_read_actor(read_descriptor_t *desc, struct page *page,
-			unsigned long offset, unsigned long size)
-{
-	char *kaddr;
-	unsigned long left, count = desc->count;
-
-	if (size > count)
-		size = count;
-
-	/*
-	 * Faults on the destination of a read are common, so do it before
-	 * taking the kmap.
-	 */
-	if (!fault_in_pages_writeable(desc->arg.buf, size)) {
-		kaddr = kmap_atomic(page);
-		left = __copy_to_user_inatomic(desc->arg.buf,
-						kaddr + offset, size);
-		kunmap_atomic(kaddr);
-		if (left == 0)
-			goto success;
-	}
-
-	/* Do it the slow way */
-	kaddr = kmap(page);
-	left = __copy_to_user(desc->arg.buf, kaddr + offset, size);
-	kunmap(page);
-
-	if (left) {
-		size -= left;
-		desc->error = -EFAULT;
-	}
-success:
-	desc->count = count - size;
-	desc->written += size;
-	desc->arg.buf += size;
-	return size;
-}
-
 /*
  * Performs necessary checks before doing a write
  * @iov:	io vector request
@@ -1372,8 +1334,8 @@ int generic_segment_checks(const struct
 }
 EXPORT_SYMBOL(generic_segment_checks);
 
-static int file_read_iter_actor(read_descriptor_t *desc, struct page *page,
-				unsigned long offset, unsigned long size)
+int file_read_iter_actor(read_descriptor_t *desc, struct page *page,
+			 unsigned long offset, unsigned long size)
 {
 	struct iov_iter *iter = desc->arg.data;
 	unsigned long copied = 0;
--- 3.8-dk/mm/shmem.c	2013-01-02 20:27:10.956550061 -0800
+++ linux/mm/shmem.c	2013-02-03 21:21:17.332510148 -0800
@@ -1463,14 +1463,23 @@ shmem_write_end(struct file *file, struc
 	return copied;
 }
 
-static void do_shmem_file_read(struct file *filp, loff_t *ppos, read_descriptor_t *desc, read_actor_t actor)
+static ssize_t shmem_file_read_iter(struct kiocb *iocb,
+				struct iov_iter *iter, loff_t pos)
 {
+	read_descriptor_t desc;
+	loff_t *ppos = &iocb->ki_pos;
+	struct file *filp = iocb->ki_filp;
 	struct inode *inode = filp->f_path.dentry->d_inode;
 	struct address_space *mapping = inode->i_mapping;
 	pgoff_t index;
 	unsigned long offset;
 	enum sgp_type sgp = SGP_READ;
 
+	desc.written = 0;
+	desc.count = iov_iter_count(iter);
+	desc.arg.data = iter;
+	desc.error = 0;
+
 	/*
 	 * Might this read be for a stacking filesystem?  Then when reading
 	 * holes of a sparse file, we actually need to allocate those pages,
@@ -1497,10 +1506,10 @@ static void do_shmem_file_read(struct fi
 				break;
 		}
 
-		desc->error = shmem_getpage(inode, index, &page, sgp, NULL);
-		if (desc->error) {
-			if (desc->error == -EINVAL)
-				desc->error = 0;
+		desc.error = shmem_getpage(inode, index, &page, sgp, NULL);
+		if (desc.error) {
+			if (desc.error == -EINVAL)
+				desc.error = 0;
 			break;
 		}
 		if (page)
@@ -1551,13 +1560,13 @@ static void do_shmem_file_read(struct fi
 		 * "pos" here (the actor routine has to update the user buffer
 		 * pointers and the remaining count).
 		 */
-		ret = actor(desc, page, offset, nr);
+		ret = file_read_iter_actor(&desc, page, offset, nr);
 		offset += ret;
 		index += offset >> PAGE_CACHE_SHIFT;
 		offset &= ~PAGE_CACHE_MASK;
 
 		page_cache_release(page);
-		if (ret != nr || !desc->count)
+		if (ret != nr || !desc.count)
 			break;
 
 		cond_resched();
@@ -1565,40 +1574,8 @@ static void do_shmem_file_read(struct fi
 
 	*ppos = ((loff_t) index << PAGE_CACHE_SHIFT) + offset;
 	file_accessed(filp);
-}
 
-static ssize_t shmem_file_aio_read(struct kiocb *iocb,
-		const struct iovec *iov, unsigned long nr_segs, loff_t pos)
-{
-	struct file *filp = iocb->ki_filp;
-	ssize_t retval;
-	unsigned long seg;
-	size_t count;
-	loff_t *ppos = &iocb->ki_pos;
-
-	retval = generic_segment_checks(iov, &nr_segs, &count, VERIFY_WRITE);
-	if (retval)
-		return retval;
-
-	for (seg = 0; seg < nr_segs; seg++) {
-		read_descriptor_t desc;
-
-		desc.written = 0;
-		desc.arg.buf = iov[seg].iov_base;
-		desc.count = iov[seg].iov_len;
-		if (desc.count == 0)
-			continue;
-		desc.error = 0;
-		do_shmem_file_read(filp, ppos, &desc, file_read_actor);
-		retval += desc.written;
-		if (desc.error) {
-			retval = retval ?: desc.error;
-			break;
-		}
-		if (desc.count > 0)
-			break;
-	}
-	return retval;
+	return desc.written ? desc.written : desc.error;
 }
 
 static ssize_t shmem_file_splice_read(struct file *in, loff_t *ppos,
@@ -2679,8 +2656,8 @@ static const struct file_operations shme
 	.llseek		= shmem_file_llseek,
 	.read		= do_sync_read,
 	.write		= do_sync_write,
-	.aio_read	= shmem_file_aio_read,
-	.aio_write	= generic_file_aio_write,
+	.read_iter	= shmem_file_read_iter,
+	.write_iter	= generic_file_write_iter,
 	.fsync		= noop_fsync,
 	.splice_read	= shmem_file_splice_read,
 	.splice_write	= generic_file_splice_write,