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Subject[PATCH 14/18] shmem: convert to using splice instead of sendfile()
Date
From: Hugh Dickins <hugh@veritas.com>

Remove shmem_file_sendfile and resurrect shmem_readpage, as used by tmpfs
to support loop and sendfile in 2.4 and 2.5. Now tmpfs can support splice,
loop and sendfile in the simplest way, using generic_file_splice_read and
generic_file_splice_write (with the aid of shmem_prepare_write).

We could make some efficiency tweaks later, if there's a real need;
but this is stable and works well as is.

Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
---
mm/shmem.c | 42 +++++++++++++++++-------------------------
1 files changed, 17 insertions(+), 25 deletions(-)

diff --git a/mm/shmem.c b/mm/shmem.c
index b6aae2b..0493e4d 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1100,9 +1100,9 @@ static int shmem_getpage(struct inode *inode, unsigned long idx,
* Normally, filepage is NULL on entry, and either found
* uptodate immediately, or allocated and zeroed, or read
* in under swappage, which is then assigned to filepage.
- * But shmem_prepare_write passes in a locked filepage,
- * which may be found not uptodate by other callers too,
- * and may need to be copied from the swappage read in.
+ * But shmem_readpage and shmem_prepare_write pass in a locked
+ * filepage, which may be found not uptodate by other callers
+ * too, and may need to be copied from the swappage read in.
*/
repeat:
if (!filepage)
@@ -1485,9 +1485,18 @@ static const struct inode_operations shmem_symlink_inode_operations;
static const struct inode_operations shmem_symlink_inline_operations;

/*
- * Normally tmpfs makes no use of shmem_prepare_write, but it
- * lets a tmpfs file be used read-write below the loop driver.
+ * Normally tmpfs avoids the use of shmem_readpage and shmem_prepare_write;
+ * but providing them allows a tmpfs file to be used for splice, sendfile, and
+ * below the loop driver, in the generic fashion that many filesystems support.
*/
+static int shmem_readpage(struct file *file, struct page *page)
+{
+ struct inode *inode = page->mapping->host;
+ int error = shmem_getpage(inode, page->index, &page, SGP_CACHE, NULL);
+ unlock_page(page);
+ return error;
+}
+
static int
shmem_prepare_write(struct file *file, struct page *page, unsigned offset, unsigned to)
{
@@ -1711,25 +1720,6 @@ static ssize_t shmem_file_read(struct file *filp, char __user *buf, size_t count
return desc.error;
}

-static ssize_t shmem_file_sendfile(struct file *in_file, loff_t *ppos,
- size_t count, read_actor_t actor, void *target)
-{
- read_descriptor_t desc;
-
- if (!count)
- return 0;
-
- desc.written = 0;
- desc.count = count;
- desc.arg.data = target;
- desc.error = 0;
-
- do_shmem_file_read(in_file, ppos, &desc, actor);
- if (desc.written)
- return desc.written;
- return desc.error;
-}
-
static int shmem_statfs(struct dentry *dentry, struct kstatfs *buf)
{
struct shmem_sb_info *sbinfo = SHMEM_SB(dentry->d_sb);
@@ -2386,6 +2376,7 @@ static const struct address_space_operations shmem_aops = {
.writepage = shmem_writepage,
.set_page_dirty = __set_page_dirty_no_writeback,
#ifdef CONFIG_TMPFS
+ .readpage = shmem_readpage,
.prepare_write = shmem_prepare_write,
.commit_write = simple_commit_write,
#endif
@@ -2399,7 +2390,8 @@ static const struct file_operations shmem_file_operations = {
.read = shmem_file_read,
.write = shmem_file_write,
.fsync = simple_sync_file,
- .sendfile = shmem_file_sendfile,
+ .splice_read = generic_file_splice_read,
+ .splice_write = generic_file_splice_write,
#endif
};

--
1.5.2.1.174.gcd03
-
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