[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.villem...@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

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