android_kernel_samsung_msm8976/arch/um/sys-i386
Jeff Dike 3d564047a5 uml: start fixing os_read_file and os_write_file
This patch starts the removal of a very old, very broken piece of code.  This
stems from the problem of passing a userspace buffer into read() or write() on
the host.  If that buffer had not yet been faulted in, read and write will
return -EFAULT.

To avoid this problem, the solution was to fault the buffer in before the
system call by touching the pages that hold the buffer by doing a copy-user of
a byte to each page.  This is obviously bogus, but it does usually work, in tt
mode, since the kernel and process are in the same address space and userspace
addresses can be accessed directly in the kernel.

In skas mode, where the kernel and process are in separate address spaces, it
is completely bogus because the userspace address, which is invalid in the
kernel, is passed into the system call instead of the corresponding physical
address, which would be valid.  Here, it appears that this code, on every host
read() or write(), tries to fault in a random process page.  This doesn't seem
to cause any correctness problems, but there is a performance impact.  This
patch, and the ones following, result in a 10-15% performance gain on a kernel
build.

This code can't be immediately tossed out because when it is, you can't log
in.  Apparently, there is some code in the console driver which depends on
this somehow.

However, we can start removing it by switching the code which does I/O using
kernel addresses to using plain read() and write().  This patch introduces
os_read_file_k and os_write_file_k for use with kernel buffers and converts
all call locations which use obvious kernel buffers to use them.  These
include I/O using buffers which are local variables which are on the stack or
kmalloc-ed.  Later patches will handle the less obvious cases, followed by a
mass conversion back to the original interface.

Signed-off-by: Jeff Dike <jdike@linux.intel.com>
Cc: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-05-07 12:13:03 -07:00
..
bug.c [PATCH] UML: add generic BUG support 2006-12-08 08:28:39 -08:00
bugs.c uml: start fixing os_read_file and os_write_file 2007-05-07 12:13:03 -07:00
checksum.S Remove obsolete #include <linux/config.h> 2006-06-30 19:25:36 +02:00
delay.c [PATCH] uml: fix unreasonably long udelay 2007-04-02 10:06:08 -07:00
fault.c uml: tidy fault code 2007-05-07 12:13:02 -07:00
ksyms.c [PATCH] uml: fix some double export warnings 2006-04-11 06:18:36 -07:00
ldt.c uml: start fixing os_read_file and os_write_file 2007-05-07 12:13:03 -07:00
Makefile [PATCH] UML: add generic BUG support 2006-12-08 08:28:39 -08:00
ptrace.c Remove obsolete #include <linux/config.h> 2006-06-30 19:25:36 +02:00
ptrace_user.c uml: remove user_util.h 2007-05-07 12:13:01 -07:00
setjmp.S [PATCH] uml: Use klibc setjmp/longjmp 2006-09-26 08:49:05 -07:00
sigcontext.c Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
signal.c uml: kernel segfaults should dump proper registers 2007-05-07 12:13:02 -07:00
stub.S [PATCH] uml: skas0 stubs now check system call return values 2005-09-05 00:06:24 -07:00
stub_segv.c [PATCH] uml: add missing __volatile__ 2006-04-19 09:13:51 -07:00
sys_call_table.S [PATCH] uml: remove unneeded time definitions 2006-06-30 11:25:38 -07:00
syscalls.c [PATCH] uml: more __user annotations 2006-06-05 12:29:17 -07:00
sysrq.c Remove all inclusions of <linux/config.h> 2006-10-04 03:38:54 -04:00
tls.c uml: no locking needed in tls.c 2007-05-07 12:13:02 -07:00
unmap.c [PATCH] Fix "Remove the use of _syscallX macros in UML" 2006-10-30 12:08:41 -08:00
user-offsets.c uml: delete HOST_FRAME_SIZE 2007-05-07 12:13:02 -07:00