get rid of legacy 'get_ds()' function

Every in-kernel use of this function defined it to KERNEL_DS (either as
an actual define, or as an inline function).  It's an entirely
historical artifact, and long long long ago used to actually read the
segment selector valueof '%ds' on x86.

Which in the kernel is always KERNEL_DS.

Inspired by a patch from Jann Horn that just did this for a very small
subset of users (the ones in fs/), along with Al who suggested a script.
I then just took it to the logical extreme and removed all the remaining
gunk.

Roughly scripted with

   git grep -l '(get_ds())' -- :^tools/ | xargs sed -i 's/(get_ds())/(KERNEL_DS)/'
   git grep -lw 'get_ds' -- :^tools/ | xargs sed -i '/^#define get_ds()/d'

plus manual fixups to remove a few unusual usage patterns, the couple of
inline function cases and to fix up a comment that had become stale.

The 'get_ds()' function remains in an x86 kvm selftest, since in user
space it actually does something relevant.

Inspired-by: Jann Horn <jannh@google.com>
Inspired-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 3 insertions, 3 deletions

diff --git a/fs/read_write.c b/fs/read_write.c
index ff3c5e6f87cf..30df848b7451 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -426,7 +426,7 @@ ssize_t kernel_read(struct file *file, void *buf, size_t count, loff_t *pos)
 	ssize_t result;
 
 	old_fs = get_fs();
-	set_fs(get_ds());
+	set_fs(KERNEL_DS);
 	/* The cast to a user pointer is valid due to the set_fs() */
 	result = vfs_read(file, (void __user *)buf, count, pos);
 	set_fs(old_fs);
@@ -499,7 +499,7 @@ ssize_t __kernel_write(struct file *file, const void *buf, size_t count, loff_t
 		return -EINVAL;
 
 	old_fs = get_fs();
-	set_fs(get_ds());
+	set_fs(KERNEL_DS);
 	p = (__force const char __user *)buf;
 	if (count > MAX_RW_COUNT)
 		count =  MAX_RW_COUNT;
@@ -521,7 +521,7 @@ ssize_t kernel_write(struct file *file, const void *buf, size_t count,
 	ssize_t res;
 
 	old_fs = get_fs();
-	set_fs(get_ds());
+	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);