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

 and output nothing if writing was requested. -100 bytes

1 files changed, 42 insertions, 37 deletions

diff --git a/miscutils/devmem.c b/miscutils/devmem.c
index 8b8edbe7c..4903b5dcb 100644
--- 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);
         }