Add a function to write one single whole page of data to an inode at a
page-aligned location (thus permitting the function to be highly optimised).
The function uses the prepare_write() and commit_write() address_space
operations to bound the actual write.
This is used by CacheFiles to store the contents of netfs pages into their
backing file pages.
Signed-Off-By: David Howells <[email protected]>
---
include/linux/fs.h | 2 +
mm/filemap.c | 87 ++++++++++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 89 insertions(+), 0 deletions(-)
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 2fe6e3f..2bb027f 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1748,6 +1748,8 @@ extern ssize_t generic_file_direct_write
unsigned long *, loff_t, loff_t *, size_t, size_t);
extern ssize_t generic_file_buffered_write(struct kiocb *, const struct iovec *,
unsigned long, loff_t, loff_t *, size_t, ssize_t);
+extern int generic_file_buffered_write_one_kernel_page(struct address_space *,
+ pgoff_t, struct page *);
extern ssize_t do_sync_read(struct file *filp, char __user *buf, size_t len, loff_t *ppos);
extern ssize_t do_sync_write(struct file *filp, const char __user *buf, size_t len, loff_t *ppos);
extern ssize_t generic_file_sendfile(struct file *, loff_t *, size_t, read_actor_t, void *);
diff --git a/mm/filemap.c b/mm/filemap.c
index 1b73d3a..b9eb8b2 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2236,6 +2236,93 @@ zero_length_segment:
}
EXPORT_SYMBOL(generic_file_buffered_write);
+/**
+ * generic_file_buffered_write_one_kernel_page - Write a single page of data to
+ * an inode
+ * @mapping - The address space of the target inode
+ * @index - The target page in the target inode to fill
+ * @source - The data to write into the target page
+ *
+ * Write the data from the source page to the page in the nominated address
+ * space at the @index specified
+ *
+ * The @source page does not need to have any association with the file or the
+ * target page offset
+ */
+int
+generic_file_buffered_write_one_kernel_page(struct address_space *mapping,
+ pgoff_t index,
+ struct page *source)
+{
+ const struct address_space_operations *a_ops = mapping->a_ops;
+ struct pagevec lru_pvec;
+ struct page *page, *cached_page = NULL;
+ long status = 0;
+
+ pagevec_init(&lru_pvec, 0);
+
+ page = __grab_cache_page(mapping, index, &cached_page, &lru_pvec);
+ if (!page) {
+ BUG_ON(cached_page);
+ return -ENOMEM;
+ }
+
+ status = a_ops->prepare_write(NULL, page, 0, PAGE_CACHE_SIZE);
+ if (unlikely(status)) {
+ loff_t isize = i_size_read(mapping->host);
+
+ if (status != AOP_TRUNCATED_PAGE)
+ unlock_page(page);
+ page_cache_release(page);
+ if (status == AOP_TRUNCATED_PAGE)
+ goto sync;
+
+ /* prepare_write() may have instantiated a few blocks outside
+ * i_size. Trim these off again.
+ */
+ if ((1ULL << (index + 1)) > isize)
+ vmtruncate(mapping->host, isize);
+ goto sync;
+ }
+
+ copy_highpage(page, source);
+ flush_dcache_page(page);
+
+ status = a_ops->commit_write(NULL, page, 0, PAGE_CACHE_SIZE);
+ if (status == AOP_TRUNCATED_PAGE) {
+ page_cache_release(page);
+ goto sync;
+ }
+
+ if (status > 0)
+ status = 0;
+
+ unlock_page(page);
+ mark_page_accessed(page);
+ page_cache_release(page);
+ if (status < 0)
+ return status;
+
+ balance_dirty_pages_ratelimited(mapping);
+ cond_resched();
+
+sync:
+ if (cached_page)
+ page_cache_release(cached_page);
+
+ /* the caller must handle O_SYNC themselves, but we handle S_SYNC and
+ * MS_SYNCHRONOUS here */
+ if (unlikely(IS_SYNC(mapping->host)) && !a_ops->writepage)
+ status = generic_osync_inode(mapping->host, mapping,
+ OSYNC_METADATA | OSYNC_DATA);
+
+ /* the caller must handle O_DIRECT for themselves */
+
+ pagevec_lru_add(&lru_pvec);
+ return status;
+}
+EXPORT_SYMBOL(generic_file_buffered_write_one_kernel_page);
+
static ssize_t
__generic_file_aio_write_nolock(struct kiocb *iocb, const struct iovec *iov,
unsigned long nr_segs, loff_t *ppos)
-
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