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/* Some code here borrowed from dmidecode, also GPLed and copyrighted by:
* (C) 2000-2002 Alan Cox <alan@redhat.com>
* (C) 2002-2005 Jean Delvare <khali@linux-fr.org>
* I (Colin Watson) copied it in reduced form rather than using dmidecode
* directly because (a) the d-i initrd is tight on space and this is much
* smaller and (b) parsing the output of dmidecode in shell is unreasonably
* painful.
*/
#include <stdlib.h>
#include <string.h>
#include <stdint.h>
#include <unistd.h>
#include <sys/mman.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>
#define WORD(x) (*(const uint16_t *)(x))
#define DWORD(x) (*(const uint32_t *)(x))
struct dmi_header
{
uint8_t type;
uint8_t length;
uint16_t handle;
};
static int checksum(const uint8_t *buf, size_t len)
{
uint8_t sum = 0;
size_t a;
for (a = 0; a < len; a++)
sum += buf[a];
return (sum == 0);
}
/* Copy a physical memory chunk into a memory buffer.
* This function allocates memory.
*/
static void *mem_chunk(size_t base, size_t len)
{
void *p;
int fd;
size_t mmoffset;
void *mmp;
fd = open("/dev/mem", O_RDONLY);
if (fd == -1)
return NULL;
p = malloc(len);
if (p == NULL)
{
close(fd);
return NULL;
}
#ifdef _SC_PAGESIZE
mmoffset = base % sysconf(_SC_PAGESIZE);
#else
mmoffset = base % getpagesize();
#endif
/* Please note that we don't use mmap() for performance reasons here,
* but to workaround problems many people encountered when trying
* to read from /dev/mem using regular read() calls.
*/
mmp = mmap(0, mmoffset + len, PROT_READ, MAP_SHARED, fd,
base - mmoffset);
if (mmp == MAP_FAILED)
{
free(p);
close(fd);
return NULL;
}
memcpy(p, mmp + mmoffset, len);
munmap(mmp, mmoffset + len);
close(fd);
return p;
}
static uint64_t dmi_table(uint32_t base, uint16_t len, uint16_t num)
{
uint8_t *buf, *data;
int i = 0;
uint64_t available = 0;
buf = mem_chunk(base, len);
if (buf == NULL)
return 0;
data = buf;
while (i < num && data + sizeof(struct dmi_header) <= buf + len)
{
uint8_t *next;
struct dmi_header *h = (struct dmi_header *)data;
/* Stop decoding at end of table marker */
if (h->type == 127)
break;
/* Look for the next handle */
next = data + h->length;
while (next - buf + 1 < len && (next[0] != 0 || next[1] != 0))
next++;
next += 2;
/* Memory Array Mapped Address */
if (h->type == 19 && h->length >= 0x0F)
{
uint64_t start, end;
start = DWORD(data + 0x04);
end = DWORD(data + 0x08);
if (end >= start)
/* output in kilobytes */
available += end - start + 1;
}
data = next;
i++;
}
free(buf);
return available;
}
static uint64_t smbios_decode(uint8_t *buf)
{
if (checksum(buf, buf[0x05]) &&
memcmp(buf + 0x10, "_DMI_", 5) == 0 &&
checksum(buf + 0x10, 0x0F))
{
return dmi_table(DWORD(buf + 0x18), WORD(buf + 0x16),
WORD(buf + 0x1C));
}
return 0;
}
static uint64_t legacy_decode(uint8_t *buf)
{
if (checksum(buf, 0x0F))
{
return dmi_table(DWORD(buf + 0x08), WORD(buf + 0x06),
WORD(buf + 0x0C));
}
return 0;
}
static uint64_t dmi_available_memory(void)
{
uint8_t *buf;
size_t fp;
uint64_t ret = 0;
buf = mem_chunk(0xF0000, 0x10000);
if (buf == NULL)
return 0;
for (fp = 0; fp <= 0xFFF0; fp += 16)
{
if (memcmp(buf + fp, "_SM_", 4) == 0 && fp <= 0xFFE0)
{
ret = smbios_decode(buf + fp);
if (ret)
break;
fp += 16;
}
else if (memcmp(buf + fp, "_DMI_", 5) == 0)
{
ret = legacy_decode(buf + fp);
if (ret)
break;
}
}
free(buf);
return ret;
}
int main(int argc, char **argv)
{
printf("%llu\n", dmi_available_memory());
return 0;
}
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