[PATCH] fw_env: keep calling read() until whole flash block is read

[Rafał Miłecki]

From: Rafał Miłecki <rafal at milecki.pl>

It's totally valid for read() to provide less bytes than requested
maximum. It may happen if there is no more data available yet or source
pushes data in small chunks.

This actually happens when trying to read env data from NVMEM device.
Kernel may provide NVMEM content in page size parts (like 4096 B).

This fixes warnings like:
Warning on /sys/bus/nvmem/devices/u-boot-env0/nvmem: Attempted to read 16384 bytes but got 4096
Warning on /sys/bus/nvmem/devices/u-boot-env0/nvmem: Attempted to read 12288 bytes but got 4096
Warning on /sys/bus/nvmem/devices/u-boot-env0/nvmem: Attempted to read 8192 bytes but got 4096

Since the main loop in flash_read_buf() is used to read blocks this
patch adds a new nested one.

Signed-off-by: Rafał Miłecki <rafal at milecki.pl>
---
 tools/env/fw_env.c | 34 +++++++++++++++-------------------
 1 file changed, 15 insertions(+), 19 deletions(-)

diff --git a/tools/env/fw_env.c b/tools/env/fw_env.c
index 0347e9d15a..90010dabd8 100644
--- a/tools/env/fw_env.c
+++ b/tools/env/fw_env.c
@@ -948,29 +948,25 @@ 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 == -1) {
-			fprintf(stderr, "Read error on %s: %s\n",
-				DEVNAME(dev), strerror(errno));
-			return -1;
-		}
+		while (readlen) {
+			rc = read(fd, buf + processed, readlen);
+			if (rc == -1) {
+				fprintf(stderr, "Read error on %s: %s\n",
+					DEVNAME(dev), strerror(errno));
+				return -1;
+			}
 #ifdef DEBUG
-		fprintf(stderr, "Read 0x%x bytes at 0x%llx on %s\n",
-			rc, (unsigned long long)blockstart + block_seek,
-			DEVNAME(dev));
+			fprintf(stderr, "Read 0x%x bytes at 0x%llx on %s\n",
+				rc, (unsigned long long)blockstart + block_seek,
+				DEVNAME(dev));
 #endif
-		processed += rc;
-		if (rc != readlen) {
-			fprintf(stderr,
-				"Warning on %s: Attempted to read %zd bytes but got %d\n",
-				DEVNAME(dev), readlen, rc);
+			processed += rc;
 			readlen -= rc;
-			block_seek += rc;
-		} else {
-			blockstart += blocklen;
-			readlen = min(blocklen, count - processed);
-			block_seek = 0;
 		}
+
+		blockstart += blocklen;
+		readlen = min(blocklen, count - processed);
+		block_seek = 0;
 	}
 
 	return processed;
-- 
2.35.3