[coreboot-gerrit] Change in ...coreboot[master]: intelvbttool: Added support for reading vbt from sysfs

[Alex Feinman (Code Review)]

Alex Feinman has uploaded this change for review. ( https://review.coreboot.org/c/coreboot/+/31531

Change subject: intelvbttool: Added support for reading vbt from sysfs
......................................................................

intelvbttool: Added support for reading vbt from sysfs

VBT on intel 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.
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 
---
M util/intelvbttool/intelvbttool.c
1 file changed, 21 insertions(+), 5 deletions(-)

git pull ssh://review.coreboot.org:29418/coreboot refs/changes/31/31531/1

diff --git a/util/intelvbttool/intelvbttool.c b/util/intelvbttool/intelvbttool.c
index 1444129..2941b42 100644
--- a/util/intelvbttool/intelvbttool.c
+++ b/util/intelvbttool/intelvbttool.c
@@ -29,6 +29,7 @@
 typedef uint16_t u16;
 typedef uint32_t u32;

+#define DEF_ALLOC 1024

typedef struct {
    u16 signature;
@@ -392,8 +393,8 @@
    	return NULL;
    }

-	const off_t size = ftell(fd);
-	if (size < 0 || size > SIZE_MAX) {
+	off_t read_size = ftell(fd);
+	if (read_size < 0 || read_size > SIZE_MAX) {
    	printerr("%s tell failed: %s\n", filename, strerror(errno));
    	fclose(fd);
    	return NULL;
@@ -405,14 +406,29 @@
    	return NULL;
    }

-	struct fileobject *fo = malloc_fo(size);
+	if ( read_size == 0 )
+		read_size = DEF_ALLOC;
+
+	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 bytes_read = 0, cb;
+	while((cb = fread(fo->data + bytes_read, 1, read_size, fd)) > 0) {
+		bytes_read += cb;
+		struct fileobject* newfo = remalloc_fo(fo, fo->size + read_size);
+		if (!newfo) {
+			fclose(fd);
+			free_fo(fo);
+			return NULL;
+		}
+		fo = newfo;
+	}
+
+	if (!bytes_read) {
    	fclose(fd);
    	free_fo(fo);
    	return NULL;
@@ -424,7 +440,7 @@
    	return NULL;
    }

-	fo->size = size;
+	fo->size = bytes_read;

return fo;
 }