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devmem: map two pages only if it is necessary

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function                                             old     new   delta
devmem_main                                          463     469      +6

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
This commit is contained in:
Denys Vlasenko 2010-04-14 13:37:25 -07:00
parent 375a8ef5ea
commit 351ef7188a
1 changed files with 14 additions and 7 deletions
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21
miscutils/devmem.c
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@ -13,9 +13,9 @@ int devmem_main(int argc UNUSED_PARAM, char **argv)
uint64_t read_result; uint64_t read_result;
uint64_t writeval = writeval; /* for compiler */ uint64_t writeval = writeval; /* for compiler */
off_t target; off_t target;
unsigned page_size = getpagesize(); unsigned page_size, mapped_size, offset_in_page;
int fd; int fd;
int width = 8 * sizeof(int); unsigned width = 8 * sizeof(int);
/* devmem ADDRESS [WIDTH [VALUE]] */ /* devmem ADDRESS [WIDTH [VALUE]] */
// TODO: options? // TODO: options?
@ -50,15 +50,22 @@ int devmem_main(int argc UNUSED_PARAM, char **argv)
if (argv[3]) if (argv[3])
writeval = bb_strtoull(argv[3], NULL, 0); writeval = bb_strtoull(argv[3], NULL, 0);
} else { /* argv[2] == NULL */ } 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--; argv--;
} }
if (errno) 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)); 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, map_base = mmap(NULL,
page_size * 2 /* in case value spans page */, mapped_size,
argv[3] ? (PROT_READ | PROT_WRITE) : PROT_READ, argv[3] ? (PROT_READ | PROT_WRITE) : PROT_READ,
MAP_SHARED, MAP_SHARED,
fd, fd,
@ -68,7 +75,7 @@ int devmem_main(int argc UNUSED_PARAM, char **argv)
// printf("Memory mapped at address %p.\n", map_base); // 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]) { if (!argv[3]) {
switch (width) { switch (width) {
@ -119,7 +126,7 @@ int devmem_main(int argc UNUSED_PARAM, char **argv)
} }
if (ENABLE_FEATURE_CLEAN_UP) { 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"); bb_perror_msg_and_die("munmap");
close(fd); close(fd);
} }