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From 351ef7188a1a2e2f154bbda6f703c2d3f4af6d79 Mon Sep 17 00:00:00 2001
From: Denys Vlasenko <vda.linux@googlemail.com>
Date: Wed, 14 Apr 2010 13:37:25 -0700
Subject: [PATCH] devmem: map two pages only if it is necessary
function old new delta
devmem_main 463 469 +6
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
---
miscutils/devmem.c | 21 ++++++++++++++-------
1 files changed, 14 insertions(+), 7 deletions(-)
diff --git a/miscutils/devmem.c b/miscutils/devmem.c
index e13dedc..39b5808 100644
--- a/miscutils/devmem.c
+++ b/miscutils/devmem.c
@@ -13,9 +13,9 @@ int devmem_main(int argc UNUSED_PARAM, char **argv)
uint64_t read_result;
uint64_t writeval = writeval; /* for compiler */
off_t target;
- unsigned page_size = getpagesize();
+ unsigned page_size, mapped_size, offset_in_page;
int fd;
- int width = 8 * sizeof(int);
+ unsigned width = 8 * sizeof(int);
/* devmem ADDRESS [WIDTH [VALUE]] */
// TODO: options?
@@ -50,15 +50,22 @@ int devmem_main(int argc UNUSED_PARAM, char **argv)
if (argv[3])
writeval = bb_strtoull(argv[3], NULL, 0);
} else { /* argv[2] == NULL */
- /* make argv[3] to be a valid thing to use */
+ /* make argv[3] to be a valid thing to fetch */
argv--;
}
if (errno)
- bb_show_usage(); /* bb_strtouXX failed */
+ bb_show_usage(); /* one of bb_strtouXX failed */
fd = xopen("/dev/mem", argv[3] ? (O_RDWR | O_SYNC) : (O_RDONLY | O_SYNC));
+ mapped_size = page_size = getpagesize();
+ offset_in_page = (unsigned)target & (page_size - 1);
+ if (offset_in_page + width > page_size) {
+ /* This access spans pages.
+ * Must map two pages to make it possible: */
+ mapped_size *= 2;
+ }
map_base = mmap(NULL,
- page_size * 2 /* in case value spans page */,
+ mapped_size,
argv[3] ? (PROT_READ | PROT_WRITE) : PROT_READ,
MAP_SHARED,
fd,
@@ -68,7 +75,7 @@ int devmem_main(int argc UNUSED_PARAM, char **argv)
// printf("Memory mapped at address %p.\n", map_base);
- virt_addr = (char*)map_base + (target & (page_size - 1));
+ virt_addr = (char*)map_base + offset_in_page;
if (!argv[3]) {
switch (width) {
@@ -119,7 +126,7 @@ int devmem_main(int argc UNUSED_PARAM, char **argv)
}
if (ENABLE_FEATURE_CLEAN_UP) {
- if (munmap(map_base, page_size * 2) == -1)
+ if (munmap(map_base, mapped_size) == -1)
bb_perror_msg_and_die("munmap");
close(fd);
}
--
1.7.1
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