[source] otrx: optimize memory usage when creating TRX image

[LEDE Commits]

rmilecki pushed a commit to source.git, branch master:
https://git.lede-project.org/6d283b8029c87590bd056617340dbdb110239415

commit 6d283b8029c87590bd056617340dbdb110239415
Author: Rafał Miłecki <rafal at milecki.pl>
AuthorDate: Mon Nov 13 23:07:46 2017 +0100

    otrx: optimize memory usage when creating TRX image
    
    There is no need to allocate buffer as big as the whole image in order
    to calculate CRC32. It's enough to use small buffer and just read file
    content block by block.
    
    Signed-off-by: Rafał Miłecki <rafal at milecki.pl>
---
 package/utils/otrx/src/otrx.c | 21 +++++++--------------
 1 file changed, 7 insertions(+), 14 deletions(-)

diff --git a/package/utils/otrx/src/otrx.c b/package/utils/otrx/src/otrx.c
index 7b02977..d08507f 100644
--- a/package/utils/otrx/src/otrx.c
+++ b/package/utils/otrx/src/otrx.c
@@ -284,7 +284,7 @@ static ssize_t otrx_create_align(FILE *trx, size_t curr_offset, size_t alignment
 
 static int otrx_create_write_hdr(FILE *trx, struct trx_header *hdr) {
 	size_t bytes, length;
-	uint8_t *buf;
+	uint8_t buf[1024];
 	uint32_t crc32;
 
 	hdr->magic = cpu_to_le32(TRX_MAGIC);
@@ -299,20 +299,13 @@ static int otrx_create_write_hdr(FILE *trx, struct trx_header *hdr) {
 
 	length = le32_to_cpu(hdr->length);
 
-	buf = malloc(length);
-	if (!buf) {
-		fprintf(stderr, "Couldn't alloc %zu B buffer\n", length);
-		return -ENOMEM;
-	}
-
-	fseek(trx, 0, SEEK_SET);
-	bytes = fread(buf, 1, length, trx);
-	if (bytes != length) {
-		fprintf(stderr, "Couldn't read %zu B of data from %s\n", length, trx_path);
-		return -ENOMEM;
+	crc32 = 0xffffffff;
+	fseek(trx, TRX_FLAGS_OFFSET, SEEK_SET);
+	length -= TRX_FLAGS_OFFSET;
+	while ((bytes = fread(buf, 1, otrx_min(sizeof(buf), length), trx)) > 0) {
+		crc32 = otrx_crc32(crc32, buf, bytes);
+		length -= bytes;
 	}
-
-	crc32 = otrx_crc32(0xffffffff, buf + TRX_FLAGS_OFFSET, length - TRX_FLAGS_OFFSET);
 	hdr->crc32 = cpu_to_le32(crc32);
 
 	fseek(trx, 0, SEEK_SET);