fs: implement kernel_write using __kernel_write

Consolidate the two in-kernel write helpers to make upcoming changes
easier.  The only difference are the missing call to rw_verify_area
in kernel_write, and an access_ok check that doesn't make sense for
kernel buffers to start with.

Signed-off-by: Christoph Hellwig <hch@lst.de>

diff --git a/fs/read_write.c b/fs/read_write.c
index 8f9fc05..5110cd1 100644 (file)
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -499,6 +499,7 @@ static ssize_t __vfs_write(struct file *file, const char __user *p,
                return -EINVAL;
 }
 
+/* caller is responsible for file_start_write/file_end_write */
 ssize_t __kernel_write(struct file *file, const void *buf, size_t count, loff_t *pos)
 {
        mm_segment_t old_fs;
@@ -528,16 +529,16 @@ ssize_t __kernel_write(struct file *file, const void *buf, size_t count, loff_t
 ssize_t kernel_write(struct file *file, const void *buf, size_t count,
                            loff_t *pos)
 {
-       mm_segment_t old_fs;
-       ssize_t res;
+       ssize_t ret;
 
-       old_fs = get_fs();
-       set_fs(KERNEL_DS);
-       /* The cast to a user pointer is valid due to the set_fs() */
-       res = vfs_write(file, (__force const char __user *)buf, count, pos);
-       set_fs(old_fs);
+       ret = rw_verify_area(WRITE, file, pos, count);
+       if (ret)
+               return ret;
 
-       return res;
+       file_start_write(file);
+       ret =  __kernel_write(file, buf, count, pos);
+       file_end_write(file);
+       return ret;
 }
 EXPORT_SYMBOL(kernel_write);