intelvbttool: Add support for reading vbt from sysfs

VBT on Intel(R) systems is available via sysfs as
    /sys/kernel/debug/dri/0/i915_vbt
However the size of this file reads as 0 causing
intelvbttool to fail. This patch implements incremental reads
with realloc for such cases or whenever the file size is not
available (e.g. reading from stdin).
After this patch is applied, intelvbttool can be used as follows:
    sudo intelvbttool -f /sys/kernel/debug/dri/0/i915_vbt -d

Change-Id: I5d17095a5747550b7115a54a7619b7294a846196
Signed-off-by: Alex Feinman <alexfeinman@hotmail.com>
Reviewed-on: https://review.coreboot.org/c/31531
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Nico Huber <nico.h@gmx.de>

1 files changed, 17 insertions, 22 deletions

diff --git a/util/intelvbttool/intelvbttool.c b/util/intelvbttool/intelvbttool.c
index 1444129b50..f8e4bda0f4 100644
--- a/util/intelvbttool/intelvbttool.c
+++ b/util/intelvbttool/intelvbttool.c
@@ -29,6 +29,7 @@ typedef uint8_t u8;
 typedef uint16_t u16;
 typedef uint32_t u32;
 
+#define DEF_ALLOC 1024
 
 typedef struct {
 	u16 signature;
@@ -380,39 +381,33 @@ static struct fileobject *malloc_fo_sub(const struct fileobject *old,
 static struct fileobject *read_file(const char *filename)
 {
 	FILE *fd = fopen(filename, "rb");
+	off_t read_size = DEF_ALLOC;
 
 	if (!fd) {
 		printerr("%s open failed: %s\n", filename, strerror(errno));
 		return NULL;
 	}
 
-	if (fseek(fd, 0, SEEK_END)) {
-		printerr("%s seek failed: %s\n", filename, strerror(errno));
-		fclose(fd);
-		return NULL;
-	}
-
-	const off_t size = ftell(fd);
-	if (size < 0 || size > SIZE_MAX) {
-		printerr("%s tell failed: %s\n", filename, strerror(errno));
-		fclose(fd);
-		return NULL;
-	}
-
-	if (fseek(fd, 0, SEEK_SET)) {
-		printerr("%s seek failed: %s\n", filename, strerror(errno));
-		fclose(fd);
-		return NULL;
-	}
-
-	struct fileobject *fo = malloc_fo(size);
+	struct fileobject *fo = malloc_fo(read_size);
 	if (!fo) {
 		printerr("malloc failed\n");
 		fclose(fd);
 		return NULL;
 	}
 
-	if (fread(fo->data, 1, size, fd) != size) {
+	off_t total_bytes_read = 0, bytes_read;
+	while ((bytes_read = fread(fo->data + total_bytes_read, 1, read_size, fd)) > 0) {
+		total_bytes_read += bytes_read;
+		struct fileobject *newfo = remalloc_fo(fo, fo->size + read_size);
+		if (!newfo) {
+			fclose(fd);
+			free_fo(fo);
+			return NULL;
+		}
+		fo = newfo;
+	}
+
+	if (!total_bytes_read) {
 		fclose(fd);
 		free_fo(fo);
 		return NULL;
@@ -424,7 +419,7 @@ static struct fileobject *read_file(const char *filename)
 		return NULL;
 	}
 
-	fo->size = size;
+	fo->size = total_bytes_read;
 
 	return fo;
 }