userland: add "hexdump" command

userland/Makefile

@@ -18,6 +18,7 @@ BIN_TARGET_NAMES := \
 	fib \
 	grep \
 	halt \
+	hexdump \
 	imgview \
 	init \
 	init-test \

userland/hexdump.c

@@ -0,0 +1,92 @@
+#include <fcntl.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+static int dump_file(int fd, bool canonical) {
+    size_t offset = 0;
+    for (;;) {
+        uint8_t buf[16];
+        ssize_t nread;
+        size_t buf_len = 0;
+        while (buf_len < sizeof(buf)) {
+            nread = read(fd, (char*)buf + buf_len, sizeof(buf) - buf_len);
+            if (nread < 0) {
+                perror("read");
+                return -1;
+            }
+            if (nread == 0)
+                break;
+            buf_len += nread;
+        }
+        if (buf_len == 0)
+            break;
+
+        printf("%08x", offset);
+        offset += 0x10;
+
+        if (canonical) {
+            putchar(' ');
+            for (size_t i = 0; i < sizeof(buf); ++i) {
+                if (i < buf_len)
+                    printf(" %02x", buf[i]);
+                else
+                    printf("   ");
+                if (i == 7)
+                    putchar(' ');
+            }
+            printf("  |");
+            for (size_t i = 0; i < buf_len; ++i)
+                putchar(isprint(buf[i]) ? buf[i] : '.');
+            printf("|\n");
+        } else {
+            for (size_t i = 0; i < buf_len; i += 2) {
+                uint16_t word = buf[i];
+                if (i + 1 < buf_len)
+                    word |= buf[i + 1] << 8;
+                printf(" %04x", word);
+            }
+            putchar('\n');
+        }
+
+        if (nread == 0)
+            break;
+    }
+    return 0;
+}
+
+int main(int argc, char* argv[]) {
+    bool canonical = false;
+    size_t num_files = 0;
+    for (int i = 1; i < argc; ++i) {
+        if (!strcmp(argv[i], "-C"))
+            canonical = true;
+        else
+            ++num_files;
+    }
+
+    if (num_files == 0) {
+        if (dump_file(STDIN_FILENO, canonical) < 0)
+            return EXIT_FAILURE;
+        return EXIT_SUCCESS;
+    }
+
+    int ret = EXIT_SUCCESS;
+    for (int i = 1; i < argc; ++i) {
+        const char* filename = argv[i];
+        if (!strcmp(filename, "-C"))
+            continue;
+        int fd =
+            strcmp(filename, "-") ? open(filename, O_RDONLY) : STDIN_FILENO;
+        if (fd < 0) {
+            perror("open");
+            continue;
+        }
+        if (dump_file(fd, canonical) < 0)
+            ret = EXIT_FAILURE;
+        if (fd != STDIN_FILENO)
+            close(fd);
+    }
+    return ret;
+}