[U-Boot] [PATCH] fw_setenv: avoid writing environment when nothing has changed

[Rasmus Villemoes]

In the case where one deletes an already-non-existing variable, or sets
a variable to the value it already has, there is no point in writing the
environment back, thus reducing wear on the underlying storage
device.

Signed-off-by: Rasmus Villemoes <rasmus.villemoes at prevas.dk>
---
 tools/env/fw_env.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/tools/env/fw_env.c b/tools/env/fw_env.c
index a5d75958e1..87aaa15198 100644
--- a/tools/env/fw_env.c
+++ b/tools/env/fw_env.c
@@ -110,6 +110,7 @@ struct environment {
 	unsigned char *flags;
 	char *data;
 	enum flag_scheme flag_scheme;
+	int dirty;
 };
 
 static struct environment environment = {
@@ -508,6 +509,9 @@ int fw_env_flush(struct env_opts *opts)
 	if (!opts)
 		opts = &default_opts;
 
+	if (!environment.dirty)
+		return 0;
+
 	/*
 	 * Update CRC
 	 */
@@ -553,7 +557,8 @@ int fw_env_write(char *name, char *value)
 
 	deleting = (oldval && !(value && strlen(value)));
 	creating = (!oldval && (value && strlen(value)));
-	overwriting = (oldval && (value && strlen(value)));
+	overwriting = (oldval && (value && strlen(value) &&
+				  strcmp(oldval, value)));
 
 	/* check for permission */
 	if (deleting) {
@@ -593,6 +598,7 @@ int fw_env_write(char *name, char *value)
 		/* Nothing to do */
 		return 0;
 
+	environment.dirty = 1;
 	if (deleting || overwriting) {
 		if (*++nxt == '\0') {
 			*env = '\0';
@@ -1441,6 +1447,7 @@ int fw_env_open(struct env_opts *opts)
 				"Warning: Bad CRC, using default environment\n");
 			memcpy(environment.data, default_environment,
 			       sizeof(default_environment));
+			environment.dirty = 1;
 		}
 	} else {
 		flag0 = *environment.flags;
@@ -1503,6 +1510,7 @@ int fw_env_open(struct env_opts *opts)
 				"Warning: Bad CRC, using default environment\n");
 			memcpy(environment.data, default_environment,
 			       sizeof(default_environment));
+			environment.dirty = 1;
 			dev_current = 0;
 		} else {
 			switch (environment.flag_scheme) {
-- 
2.16.4