devmem: make it more script-friendly; don't do any reads

 and output nothing if writing was requested. -100 bytes

diff --git a/miscutils/devmem.c b/miscutils/devmem.c
index 8b8edbe..4903b5d 100644 (file)
--- a/miscutils/devmem.c
+++ b/miscutils/devmem.c
@@ -6,9 +6,6 @@
 
 #include "libbb.h"
 
-#define DEVMEM_MAP_SIZE 4096
-#define DEVMEM_MAP_MASK (off_t)(DEVMEM_MAP_SIZE - 1)
-
 int devmem_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 int devmem_main(int argc UNUSED_PARAM, char **argv)
 {
@@ -16,10 +13,16 @@ 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();
        int fd;
        int width = 8 * sizeof(int);
 
        /* devmem ADDRESS [WIDTH [VALUE]] */
+// TODO: options?
+// -r: read and output only the value in hex, with 0x prefix
+// -w: write only, no reads before or after, and no output
+// or make this behavior default?
+// Let's try this and see how users react.
 
        /* ADDRESS */
        if (!argv[1])
@@ -54,67 +57,69 @@ int devmem_main(int argc UNUSED_PARAM, char **argv)
                bb_show_usage(); /* bb_strtouXX failed */
 
        fd = xopen("/dev/mem", argv[3] ? (O_RDWR | O_SYNC) : (O_RDONLY | O_SYNC));
-
        map_base = mmap(NULL,
-                       DEVMEM_MAP_SIZE * 2 /* in case value spans page */,
+                       page_size * 2 /* in case value spans page */,
                        argv[3] ? (PROT_READ | PROT_WRITE) : PROT_READ,
                        MAP_SHARED,
                        fd,
-                       target & ~DEVMEM_MAP_MASK);
+                       target & ~(off_t)(page_size - 1));
        if (map_base == MAP_FAILED)
                bb_perror_msg_and_die("mmap");
 
 //     printf("Memory mapped at address %p.\n", map_base);
 
-       virt_addr = (char*)map_base + (target & DEVMEM_MAP_MASK);
-
-       switch (width) {
-       case 8:
-               read_result = *(volatile uint8_t*)virt_addr;
-               break;
-       case 16:
-               read_result = *(volatile uint16_t*)virt_addr;
-               break;
-       case 32:
-               read_result = *(volatile uint32_t*)virt_addr;
-               break;
-       case 64:
-               read_result = *(volatile uint64_t*)virt_addr;
-               break;
-       default:
-               bb_error_msg_and_die("bad width");
-       }
-
-       printf("Value at address 0x%"OFF_FMT"X (%p): 0x%llX\n",
-                       target, virt_addr,
-                       (unsigned long long)read_result);
+       virt_addr = (char*)map_base + (target & (page_size - 1));
 
-       if (argv[3]) {
+       if (!argv[3]) {
                switch (width) {
                case 8:
-                       *(volatile uint8_t*)virt_addr = writeval;
                        read_result = *(volatile uint8_t*)virt_addr;
                        break;
                case 16:
-                       *(volatile uint16_t*)virt_addr = writeval;
                        read_result = *(volatile uint16_t*)virt_addr;
                        break;
                case 32:
-                       *(volatile uint32_t*)virt_addr = writeval;
                        read_result = *(volatile uint32_t*)virt_addr;
                        break;
                case 64:
-                       *(volatile uint64_t*)virt_addr = writeval;
                        read_result = *(volatile uint64_t*)virt_addr;
                        break;
+               default:
+                       bb_error_msg_and_die("bad width");
+               }
+//             printf("Value at address 0x%"OFF_FMT"X (%p): 0x%llX\n",
+//                     target, virt_addr,
+//                     (unsigned long long)read_result);
+               /* Zero-padded output shows the width of access just done */
+               printf("0x%0*llX\n", (width >> 2), (unsigned long long)read_result);
+       } else {
+               switch (width) {
+               case 8:
+                       *(volatile uint8_t*)virt_addr = writeval;
+//                     read_result = *(volatile uint8_t*)virt_addr;
+                       break;
+               case 16:
+                       *(volatile uint16_t*)virt_addr = writeval;
+//                     read_result = *(volatile uint16_t*)virt_addr;
+                       break;
+               case 32:
+                       *(volatile uint32_t*)virt_addr = writeval;
+//                     read_result = *(volatile uint32_t*)virt_addr;
+                       break;
+               case 64:
+                       *(volatile uint64_t*)virt_addr = writeval;
+//                     read_result = *(volatile uint64_t*)virt_addr;
+                       break;
+               default:
+                       bb_error_msg_and_die("bad width");
                }
-               printf("Written 0x%llX; readback 0x%llX\n",
-                               (unsigned long long)writeval,
-                               (unsigned long long)read_result);
+//             printf("Written 0x%llX; readback 0x%llX\n",
+//                             (unsigned long long)writeval,
+//                             (unsigned long long)read_result);
        }
 
        if (ENABLE_FEATURE_CLEAN_UP) {
-               if (munmap(map_base, DEVMEM_MAP_SIZE) == -1)
+               if (munmap(map_base, page_size) == -1)
                        bb_perror_msg_and_die("munmap");
                close(fd);
        }