Although O_SYNC is what you want 99% of the time, there is also a use
for not supplying the flag. See drivers/char/mem.c's uncached_access().
The big question here is probably the bikeshed issue of whether to name
the option after what it does (disable the O_SYNC flag) or _why_ you're
doing that. I opted for the former on the basis of "given the -f
argument, you're not necessarily talking to the /dev/mem driver, and
other drivers might use this for other things", even though I'm not
aware of any such driver personally. (Also, it's the shorter name!)
---
toys/other/devmem.c | 15 +++++++++------
1 file changed, 9 insertions(+), 6 deletions(-)
From 4ec6099d0ef4872b1bb51e89c637a4a35c879be9 Mon Sep 17 00:00:00 2001
From: Elliott Hughes <e...@google.com>
Date: Thu, 1 Aug 2024 12:22:15 -0400
Subject: [PATCH] devmem: add --no-sync option.
Although O_SYNC is what you want 99% of the time, there is also a use
for not supplying the flag. See drivers/char/mem.c's uncached_access().
The big question here is probably the bikeshed issue of whether to name
the option after what it does (disable the O_SYNC flag) or _why_ you're
doing that. I opted for the former on the basis of "given the -f
argument, you're not necessarily talking to the /dev/mem driver, and
other drivers might use this for other things", even though I'm not
aware of any such driver personally. (Also, it's the shorter name!)
---
toys/other/devmem.c | 15 +++++++++------
1 file changed, 9 insertions(+), 6 deletions(-)
diff --git a/toys/other/devmem.c b/toys/other/devmem.c
index 7fe427f0..9f9a9e03 100644
--- a/toys/other/devmem.c
+++ b/toys/other/devmem.c
@@ -2,18 +2,19 @@
*
* Copyright 2019 The Android Open Source Project
-USE_DEVMEM(NEWTOY(devmem, "<1f:", TOYFLAG_USR|TOYFLAG_SBIN))
+USE_DEVMEM(NEWTOY(devmem, "<1(no-sync)f:", TOYFLAG_USR|TOYFLAG_SBIN))
config DEVMEM
bool "devmem"
default y
help
- usage: devmem -f FILE ADDR [WIDTH [DATA...]]
+ usage: devmem [-f FILE] ADDR [WIDTH [DATA...]]
Read/write physical addresses. WIDTH is 1, 2, 4, or 8 bytes (default 4).
Prefix ADDR with 0x for hexadecimal, output is in same base as address.
- -f FILE File to operate on (default /dev/mem)
+ -f FILE File to operate on (default /dev/mem)
+ --no-sync Don't open the file with O_SYNC (for cached access)
*/
#define FOR_devmem
@@ -40,7 +41,8 @@ unsigned long xatolu(char *str, int bytes)
void devmem_main(void)
{
- int writing = toys.optc > 2, page_size = sysconf(_SC_PAGESIZE), bytes = 4, fd;
+ int writing = toys.optc > 2, page_size = sysconf(_SC_PAGESIZE), bytes = 4, fd,
+ flags;
unsigned long data = 0, map_off, map_len,
addr = xatolu(*toys.optargs, sizeof(long));
char *sizes = sizeof(long)==8 ? "1248" : "124";
@@ -57,8 +59,9 @@ void devmem_main(void)
// Map in just enough.
if (CFG_TOYBOX_FORK) {
- fd = xopen(TT.f ?: "/dev/mem", (writing ? O_RDWR : O_RDONLY) | O_SYNC);
-
+ flags = writing ? O_RDWR : O_RDONLY;
+ if (!FLAG(no_sync)) flags |= O_SYNC;
+ fd = xopen(TT.f ?: "/dev/mem", flags);
map_off = addr & ~(page_size - 1ULL);
map_len = (addr+bytes-map_off);
map = xmmap(0, map_len, writing ? PROT_WRITE : PROT_READ, MAP_SHARED, fd,
--
2.46.0.rc1.232.g9752f9e123-goog
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