util/nvmutil: added a "cat" command

with this, you can read 16KB and 128KB files, and output
them to stdout, but it outputs 8KB

for example:

./nvmutil gbe128.bin > gbe8.bin

now you have a 8KB file

i could probably easily add cat16 and cat128 too.

nvmutil reads two 4KB parts regardless of GbE file
size (one from the first 4KB of each half of the
file), so this was easy to implement.

Signed-off-by: Leah Rowe <leah@libreboot.org>

util/nvmutil/nvmutil.c

@@ -120,6 +120,7 @@ static void write_mac_part(size_t partnum);
 static void cmd_helper_dump(void);
 static void print_mac_from_nvm(size_t partnum);
 static void hexdump(size_t partnum);
+static void cmd_helper_cat(void);
 static void write_gbe_file(void);
 static void override_part_modified(void);
 static void set_checksum(size_t part);
@@ -236,6 +237,7 @@ enum {
 	CMD_SETMAC,
 	CMD_SWAP,
 	CMD_COPY,
+	CMD_CAT
 };
 
 /*
@@ -316,6 +318,12 @@ static const struct commands command[] = {
 	    ARG_PART,
 	    CHECKSUM_READ, SKIP_CHECKSUM_WRITE,
 	    GBE_PART_SIZE },
+
+	{ CMD_CAT, "cat", cmd_helper_cat, ARGC_3,
+	    NO_INVERT, SET_MOD_OFF,
+	    ARG_NOPART,
+	    SKIP_CHECKSUM_READ, SKIP_CHECKSUM_WRITE,
+	    GBE_PART_SIZE },
 };
 
 #define MAX_CMD_LEN 50
@@ -694,9 +702,6 @@ read_gbe_file_part(size_t p)
 
 	if (rc != (ssize_t)gbe_rw_size)
 		err(ECANCELED, "%s: Partial read from p%zu", fname, p);
-
-	printf("%s: Read %zu bytes from p%zu\n",
-	    fname, gbe_rw_size, p);
 }
 
 static ssize_t
@@ -1083,6 +1088,19 @@ hexdump(size_t partnum)
 	}
 }
 
+static void
+cmd_helper_cat(void)
+{
+	size_t wc = 0;
+	ssize_t w;
+
+	fflush(NULL);
+
+	for (wc = 0; wc < sizeof(buf); wc += w)
+		if ((w = write(STDOUT_FILENO, buf + wc, sizeof(buf) - wc)) < 1)
+			err(EIO, "%s: stdout", fname);
+}
+
 static void
 write_gbe_file(void)
 {