USER_DS vs oldfs

USER_DS vs oldfs

[Matthew Wilcox]

A common idiom in the compat code is:

                old_fs = get_fs();
                set_fs(KERNEL_DS);
                ret = sys_fcntl(fd, (cmd == F_GETLK64) ? F_GETLK :
                                ((cmd == F_SETLK64) ? F_SETLK : F_SETLKW),
                                (unsigned long)&f);
                set_fs(old_fs);

Surely we know that the current 'fs' is USER_DS and so we could simply do:

                set_fs(KERNEL_DS);
                ret = sys_fcntl(fd, (cmd == F_GETLK64) ? F_GETLK :
                                ((cmd == F_SETLK64) ? F_SETLK : F_SETLKW),
                                (unsigned long)&f);
                set_fs(USER_DS);

-- 
"Next the statesmen will invent cheap lies, putting the blame upon 
the nation that is attacked, and every man will be glad of those
conscience-soothing falsities, and will diligently study them, and refuse
to examine any refutations of them; and thus he will by and by convince 
himself that the war is just, and will thank God for the better sleep 
he enjoys after this process of grotesque self-deception." -- Mark Twain