splice: implement default splice_read method
Miklos Szeredi [Thu, 7 May 2009 13:37:36 +0000 (15:37 +0200)]
If f_op->splice_read() is not implemented, fall back to a plain read.
Use vfs_readv() to read into previously allocated pages.

This will allow splice and functions using splice, such as the loop
device, to work on all filesystems.  This includes "direct_io" files
in fuse which bypass the page cache.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

drivers/block/loop.c
fs/coda/file.c
fs/pipe.c
fs/read_write.c
fs/splice.c
include/linux/fs.h
include/linux/pipe_fs_i.h

index 9ca4bb0..801f4ab 100644 (file)
@@ -709,10 +709,6 @@ static int loop_change_fd(struct loop_device *lo, struct block_device *bdev,
        if (!S_ISREG(inode->i_mode) && !S_ISBLK(inode->i_mode))
                goto out_putf;
 
-       /* new backing store needs to support loop (eg splice_read) */
-       if (!inode->i_fop->splice_read)
-               goto out_putf;
-
        /* size of the new backing store needs to be the same */
        if (get_loop_size(lo, file) != get_loop_size(lo, old_file))
                goto out_putf;
@@ -788,12 +784,7 @@ static int loop_set_fd(struct loop_device *lo, fmode_t mode,
        error = -EINVAL;
        if (S_ISREG(inode->i_mode) || S_ISBLK(inode->i_mode)) {
                const struct address_space_operations *aops = mapping->a_ops;
-               /*
-                * If we can't read - sorry. If we only can't write - well,
-                * it's going to be read-only.
-                */
-               if (!file->f_op->splice_read)
-                       goto out_putf;
+
                if (aops->write_begin)
                        lo_flags |= LO_FLAGS_USE_AOPS;
                if (!(lo_flags & LO_FLAGS_USE_AOPS) && !file->f_op->write)
index 6a347fb..ffd4281 100644 (file)
@@ -47,6 +47,8 @@ coda_file_splice_read(struct file *coda_file, loff_t *ppos,
                      struct pipe_inode_info *pipe, size_t count,
                      unsigned int flags)
 {
+       ssize_t (*splice_read)(struct file *, loff_t *,
+                              struct pipe_inode_info *, size_t, unsigned int);
        struct coda_file_info *cfi;
        struct file *host_file;
 
@@ -54,10 +56,11 @@ coda_file_splice_read(struct file *coda_file, loff_t *ppos,
        BUG_ON(!cfi || cfi->cfi_magic != CODA_MAGIC);
        host_file = cfi->cfi_container;
 
-       if (!host_file->f_op || !host_file->f_op->splice_read)
-               return -EINVAL;
+       splice_read = host_file->f_op->splice_read;
+       if (!splice_read)
+               splice_read = default_file_splice_read;
 
-       return host_file->f_op->splice_read(host_file, ppos, pipe, count,flags);
+       return splice_read(host_file, ppos, pipe, count, flags);
 }
 
 static ssize_t
index 13414ec..f7dd21a 100644 (file)
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -302,6 +302,20 @@ int generic_pipe_buf_confirm(struct pipe_inode_info *info,
        return 0;
 }
 
+/**
+ * generic_pipe_buf_release - put a reference to a &struct pipe_buffer
+ * @pipe:      the pipe that the buffer belongs to
+ * @buf:       the buffer to put a reference to
+ *
+ * Description:
+ *     This function releases a reference to @buf.
+ */
+void generic_pipe_buf_release(struct pipe_inode_info *pipe,
+                             struct pipe_buffer *buf)
+{
+       page_cache_release(buf->page);
+}
+
 static const struct pipe_buf_operations anon_pipe_buf_ops = {
        .can_merge = 1,
        .map = generic_pipe_buf_map,
index 9d1e76b..6c8c55d 100644 (file)
@@ -805,12 +805,6 @@ static ssize_t do_sendfile(int out_fd, int in_fd, loff_t *ppos,
                goto out;
        if (!(in_file->f_mode & FMODE_READ))
                goto fput_in;
-       retval = -EINVAL;
-       in_inode = in_file->f_path.dentry->d_inode;
-       if (!in_inode)
-               goto fput_in;
-       if (!in_file->f_op || !in_file->f_op->splice_read)
-               goto fput_in;
        retval = -ESPIPE;
        if (!ppos)
                ppos = &in_file->f_pos;
@@ -834,6 +828,7 @@ static ssize_t do_sendfile(int out_fd, int in_fd, loff_t *ppos,
        retval = -EINVAL;
        if (!out_file->f_op || !out_file->f_op->sendpage)
                goto fput_out;
+       in_inode = in_file->f_path.dentry->d_inode;
        out_inode = out_file->f_path.dentry->d_inode;
        retval = rw_verify_area(WRITE, out_file, &out_file->f_pos, count);
        if (retval < 0)
index e405cf5..3bd9cb2 100644 (file)
@@ -507,9 +507,116 @@ ssize_t generic_file_splice_read(struct file *in, loff_t *ppos,
 
        return ret;
 }
-
 EXPORT_SYMBOL(generic_file_splice_read);
 
+static const struct pipe_buf_operations default_pipe_buf_ops = {
+       .can_merge = 0,
+       .map = generic_pipe_buf_map,
+       .unmap = generic_pipe_buf_unmap,
+       .confirm = generic_pipe_buf_confirm,
+       .release = generic_pipe_buf_release,
+       .steal = generic_pipe_buf_steal,
+       .get = generic_pipe_buf_get,
+};
+
+static ssize_t kernel_readv(struct file *file, const struct iovec *vec,
+                           unsigned long vlen, loff_t offset)
+{
+       mm_segment_t old_fs;
+       loff_t pos = offset;
+       ssize_t res;
+
+       old_fs = get_fs();
+       set_fs(get_ds());
+       /* The cast to a user pointer is valid due to the set_fs() */
+       res = vfs_readv(file, (const struct iovec __user *)vec, vlen, &pos);
+       set_fs(old_fs);
+
+       return res;
+}
+
+ssize_t default_file_splice_read(struct file *in, loff_t *ppos,
+                                struct pipe_inode_info *pipe, size_t len,
+                                unsigned int flags)
+{
+       unsigned int nr_pages;
+       unsigned int nr_freed;
+       size_t offset;
+       struct page *pages[PIPE_BUFFERS];
+       struct partial_page partial[PIPE_BUFFERS];
+       struct iovec vec[PIPE_BUFFERS];
+       pgoff_t index;
+       ssize_t res;
+       size_t this_len;
+       int error;
+       int i;
+       struct splice_pipe_desc spd = {
+               .pages = pages,
+               .partial = partial,
+               .flags = flags,
+               .ops = &default_pipe_buf_ops,
+               .spd_release = spd_release_page,
+       };
+
+       index = *ppos >> PAGE_CACHE_SHIFT;
+       offset = *ppos & ~PAGE_CACHE_MASK;
+       nr_pages = (len + offset + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
+
+       for (i = 0; i < nr_pages && i < PIPE_BUFFERS && len; i++) {
+               struct page *page;
+
+               page = alloc_page(GFP_HIGHUSER);
+               error = -ENOMEM;
+               if (!page)
+                       goto err;
+
+               this_len = min_t(size_t, len, PAGE_CACHE_SIZE - offset);
+               vec[i].iov_base = (void __user *) kmap(page);
+               vec[i].iov_len = this_len;
+               pages[i] = page;
+               spd.nr_pages++;
+               len -= this_len;
+               offset = 0;
+       }
+
+       res = kernel_readv(in, vec, spd.nr_pages, *ppos);
+       if (res < 0)
+               goto err;
+
+       error = 0;
+       if (!res)
+               goto err;
+
+       nr_freed = 0;
+       for (i = 0; i < spd.nr_pages; i++) {
+               kunmap(pages[i]);
+               this_len = min_t(size_t, vec[i].iov_len, res);
+               partial[i].offset = 0;
+               partial[i].len = this_len;
+               if (!this_len) {
+                       __free_page(pages[i]);
+                       pages[i] = NULL;
+                       nr_freed++;
+               }
+               res -= this_len;
+       }
+       spd.nr_pages -= nr_freed;
+
+       res = splice_to_pipe(pipe, &spd);
+       if (res > 0)
+               *ppos += res;
+
+       return res;
+
+err:
+       for (i = 0; i < spd.nr_pages; i++) {
+               kunmap(pages[i]);
+               __free_page(pages[i]);
+       }
+       return error;
+}
+EXPORT_SYMBOL(default_file_splice_read);
+
 /*
  * Send 'sd->len' bytes to socket from 'sd->file' at position 'sd->pos'
  * using sendpage(). Return the number of bytes sent.
@@ -933,11 +1040,10 @@ static long do_splice_to(struct file *in, loff_t *ppos,
                         struct pipe_inode_info *pipe, size_t len,
                         unsigned int flags)
 {
+       ssize_t (*splice_read)(struct file *, loff_t *,
+                              struct pipe_inode_info *, size_t, unsigned int);
        int ret;
 
-       if (unlikely(!in->f_op || !in->f_op->splice_read))
-               return -EINVAL;
-
        if (unlikely(!(in->f_mode & FMODE_READ)))
                return -EBADF;
 
@@ -945,7 +1051,11 @@ static long do_splice_to(struct file *in, loff_t *ppos,
        if (unlikely(ret < 0))
                return ret;
 
-       return in->f_op->splice_read(in, ppos, pipe, len, flags);
+       splice_read = in->f_op->splice_read;
+       if (!splice_read)
+               splice_read = default_file_splice_read;
+
+       return splice_read(in, ppos, pipe, len, flags);
 }
 
 /**
index 5bed436..d926c2b 100644 (file)
@@ -2204,6 +2204,8 @@ extern int generic_segment_checks(const struct iovec *iov,
 /* fs/splice.c */
 extern ssize_t generic_file_splice_read(struct file *, loff_t *,
                struct pipe_inode_info *, size_t, unsigned int);
+extern ssize_t default_file_splice_read(struct file *, loff_t *,
+               struct pipe_inode_info *, size_t, unsigned int);
 extern ssize_t generic_file_splice_write(struct pipe_inode_info *,
                struct file *, loff_t *, size_t, unsigned int);
 extern ssize_t generic_splice_sendpage(struct pipe_inode_info *pipe,
index c8f0385..b43a9e0 100644 (file)
@@ -152,5 +152,6 @@ void generic_pipe_buf_unmap(struct pipe_inode_info *, struct pipe_buffer *, void
 void generic_pipe_buf_get(struct pipe_inode_info *, struct pipe_buffer *);
 int generic_pipe_buf_confirm(struct pipe_inode_info *, struct pipe_buffer *);
 int generic_pipe_buf_steal(struct pipe_inode_info *, struct pipe_buffer *);
+void generic_pipe_buf_release(struct pipe_inode_info *, struct pipe_buffer *);
 
 #endif