Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote:
> > I don't think "write_one_page" sounds like a particularly good new
> > API addition.
>
> I also thing it's not a nice one. I still haven't seen a really good
> explanation of why it can't just use plain ->write
So, I can apply the attached patch. It opens a file each time it wants to
write a page and then closes it again, but it's the best way to avoid the
ENFILE problem. I'm benchmarking it at the moment.
David
---
diff --git a/fs/cachefiles/rdwr.c b/fs/cachefiles/rdwr.c
index 84bb8b7..a69787e 100644
--- a/fs/cachefiles/rdwr.c
+++ b/fs/cachefiles/rdwr.c
@@ -9,6 +9,8 @@
* 2 of the Licence, or (at your option) any later version.
*/
+#include <linux/mount.h>
+#include <linux/file.h>
#include "internal.h"
/*
@@ -796,7 +798,11 @@ int cachefiles_allocate_pages(struct fscache_retrieval *op,
int cachefiles_write_page(struct fscache_storage *op, struct page *page)
{
struct cachefiles_object *object;
- struct address_space *mapping;
+ struct cachefiles_cache *cache;
+ mm_segment_t old_fs;
+ struct file *file;
+ loff_t pos;
+ void *data;
int ret;
ASSERT(op != NULL);
@@ -814,13 +820,33 @@ int cachefiles_write_page(struct fscache_storage *op, struct page *page)
ASSERT(S_ISREG(object->backer->d_inode->i_mode));
- /* copy the page to ext3 and let it store it in its own time */
- mapping = object->backer->d_inode->i_mapping;
- ret = -EIO;
- if (mapping->a_ops->write_one_page) {
- ret = mapping->a_ops->write_one_page(mapping, page->index,
- page);
- _debug("write_one_page -> %d", ret);
+ cache = container_of(object->fscache.cache,
+ struct cachefiles_cache, cache);
+
+ /* write the page to the backing filesystem and let it store it in its
+ * own time */
+ dget(object->backer);
+ mntget(cache->mnt);
+ file = dentry_open(object->backer, cache->mnt, O_RDWR,
+ cache->cache_cred);
+ if (IS_ERR(file)) {
+ ret = PTR_ERR(file);
+ } else {
+ ret = -EIO;
+ if (file->f_op->write) {
+ pos = (loff_t) page->index << PAGE_SHIFT;
+ data = kmap(page);
+ old_fs = get_fs();
+ set_fs(KERNEL_DS);
+ ret = file->f_op->write(
+ file, (const void __user *) data, PAGE_SIZE,
+ &pos);
+ set_fs(old_fs);
+ kunmap(page);
+ if (ret != PAGE_SIZE)
+ ret = -EIO;
+ }
+ fput(file);
}
if (ret < 0) {
--
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