[PATCH] splice: add optional input and output offsets

add optional input and output offsets to sys_splice(), for seekable file
descriptors:

 asmlinkage long sys_splice(int fd_in, loff_t __user *off_in,
                            int fd_out, loff_t __user *off_out,
                            size_t len, unsigned int flags);

semantics are straightforward: f_pos will be updated with the offset
provided by user-space, before the splice transfer is about to begin.
Providing a NULL offset pointer means the existing f_pos will be used
(and updated in situ).  Providing an offset for a pipe results in
-ESPIPE. Providing an invalid offset pointer results in -EFAULT.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Jens Axboe <axboe@suse.de>

1 files changed, 41 insertions, 13 deletions

diff --git a/fs/splice.c b/fs/splice.c
index ed91a62402e..a5326127aad 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -680,7 +680,8 @@ EXPORT_SYMBOL(generic_splice_sendpage);
  * Attempt to initiate a splice from pipe to file.
  */
 static long do_splice_from(struct pipe_inode_info *pipe, struct file *out,
-                           size_t len, unsigned int flags)
+                           loff_t __user *off_out, size_t len,
+                           unsigned int flags)
 {
         loff_t pos;
         int ret;
@@ -691,7 +692,11 @@ static long do_splice_from(struct pipe_inode_info *pipe, struct file *out,
         if (!(out->f_mode & FMODE_WRITE))
                 return -EBADF;
 
+        if (off_out && copy_from_user(&out->f_pos, off_out, sizeof(loff_t)))
+                return -EFAULT;
+
         pos = out->f_pos;
+
         ret = rw_verify_area(WRITE, out, &pos, len);
         if (unlikely(ret < 0))
                 return ret;
@@ -702,8 +707,9 @@ static long do_splice_from(struct pipe_inode_info *pipe, struct file *out,
 /*
  * Attempt to initiate a splice from a file to a pipe.
  */
-static long do_splice_to(struct file *in, struct pipe_inode_info *pipe,
-                         size_t len, unsigned int flags)
+static long do_splice_to(struct file *in, loff_t __user *off_in,
+                         struct pipe_inode_info *pipe, size_t len,
+                         unsigned int flags)
 {
         loff_t pos, isize, left;
         int ret;
@@ -714,7 +720,11 @@ static long do_splice_to(struct file *in, struct pipe_inode_info *pipe,
         if (!(in->f_mode & FMODE_READ))
                 return -EBADF;
 
+        if (off_in && copy_from_user(&in->f_pos, off_in, sizeof(loff_t)))
+                return -EFAULT;
+
         pos = in->f_pos;
+
         ret = rw_verify_area(READ, in, &pos, len);
         if (unlikely(ret < 0))
                 return ret;
@@ -733,23 +743,39 @@ static long do_splice_to(struct file *in, struct pipe_inode_info *pipe,
 /*
  * Determine where to splice to/from.
  */
-static long do_splice(struct file *in, struct file *out, size_t len,
-                      unsigned int flags)
+static long do_splice(struct file *in, loff_t __user *off_in,
+                      struct file *out, loff_t __user *off_out,
+                      size_t len, unsigned int flags)
 {
         struct pipe_inode_info *pipe;
 
+        if (off_out && out->f_op->llseek == no_llseek)
+                return -EINVAL;
+        if (off_in && in->f_op->llseek == no_llseek)
+                return -EINVAL;
+
         pipe = in->f_dentry->d_inode->i_pipe;
-        if (pipe)
-                return do_splice_from(pipe, out, len, flags);
+        if (pipe) {
+                if (off_in)
+                        return -ESPIPE;
+
+                return do_splice_from(pipe, out, off_out, len, flags);
+        }
 
         pipe = out->f_dentry->d_inode->i_pipe;
-        if (pipe)
-                return do_splice_to(in, pipe, len, flags);
+        if (pipe) {
+                if (off_out)
+                        return -ESPIPE;
+
+                return do_splice_to(in, off_in, pipe, len, flags);
+        }
 
         return -EINVAL;
 }
 
-asmlinkage long sys_splice(int fdin, int fdout, size_t len, unsigned int flags)
+asmlinkage long sys_splice(int fd_in, loff_t __user *off_in,
+                           int fd_out, loff_t __user *off_out,
+                           size_t len, unsigned int flags)
 {
         long error;
         struct file *in, *out;
@@ -759,13 +785,15 @@ asmlinkage long sys_splice(int fdin, int fdout, size_t len, unsigned int flags)
                 return 0;
 
         error = -EBADF;
-        in = fget_light(fdin, &fput_in);
+        in = fget_light(fd_in, &fput_in);
         if (in) {
                 if (in->f_mode & FMODE_READ) {
-                        out = fget_light(fdout, &fput_out);
+                        out = fget_light(fd_out, &fput_out);
                         if (out) {
                                 if (out->f_mode & FMODE_WRITE)
-                                        error = do_splice(in, out, len, flags);
+                                        error = do_splice(in, off_in,
+                                                          out, off_out,
+                                                          len, flags);
                                 fput_light(out, fput_out);
                         }
                 }