[U-Boot] [PATCH 04/12] tools/env: Reduce the impact on real-time processes

[Joe Hershberger]

Modify fw_printenv to read in chunks of 0x20 at a time.

Signed-off-by: Joe Hershberger <joe.hershberger at ni.com>
---
 tools/env/fw_env.c | 25 ++++++++++++++++++++-----
 1 file changed, 20 insertions(+), 5 deletions(-)

diff --git a/tools/env/fw_env.c b/tools/env/fw_env.c
index 8bb7f9a..9ecc22a 100644
--- a/tools/env/fw_env.c
+++ b/tools/env/fw_env.c
@@ -45,6 +45,8 @@
 
 #include "fw_env.h"
 
+#define MAX_BYTES_PER_READ 0x20
+
 #define WHITESPACE(c) ((c == '\t') || (c == ' '))
 
 #define min(x, y) ({				\
@@ -671,6 +673,7 @@ static int flash_read_buf (int dev, int fd, void *buf, size_t count,
 	size_t blocklen;	/* erase / write length - one block on NAND,
 				   0 on NOR */
 	size_t processed = 0;	/* progress counter */
+	size_t bytesread = 0;	/* bytes read so far */
 	size_t readlen = count;	/* current read length */
 	off_t top_of_range;	/* end of the last block we may use */
 	off_t block_seek;	/* offset inside the current block to the start
@@ -730,11 +733,23 @@ static int flash_read_buf (int dev, int fd, void *buf, size_t count,
 		 */
 		lseek (fd, blockstart + block_seek, SEEK_SET);
 
-		rc = read (fd, buf + processed, readlen);
-		if (rc != readlen) {
-			fprintf (stderr, "Read error on %s: %s\n",
-				 DEVNAME (dev), strerror (errno));
-			return -1;
+		/*
+		* Break reads up into very small chunks so fw_printenv doesn't
+		* block the kernel long enough to starve other kernel tasks.
+		*/
+		bytesread = 0;
+		while (bytesread < readlen) {
+			size_t bytestoread = readlen - bytesread;
+
+			if (bytestoread > MAX_BYTES_PER_READ)
+				bytestoread = MAX_BYTES_PER_READ;
+			rc = read(fd, buf + processed + bytesread, bytestoread);
+			if (rc != bytestoread) {
+				fprintf(stderr, "Read error on %s: %s\n",
+					 DEVNAME(dev), strerror(errno));
+				return -1;
+			}
+			bytesread += bytestoread;
 		}
 #ifdef DEBUG
 		fprintf (stderr, "Read 0x%x bytes at 0x%llx\n",
-- 
1.7.11.5