shmem: convert to using splice instead of sendfile()

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>

1 files changed, 17 insertions, 25 deletions

diff --git a/mm/shmem.c b/mm/shmem.c
index b6aae2b33393..0493e4d0bcaa 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
 };