barebox-state: have the --set option to avoid writes if possible

barebox-state --set always dirties the state when successful. Users
seeking to conserve write cycles thus have to --get the variable in
question first to check whether to write it. Make life of such users
easier by having barebox-state support this out-of-the-box.

This allows users to fire and forget execute barebox-state.

This arguably should have been the behavior from the beginning,
the state implementation shared by barebox and dt-utils already
marks the state dirty if buckets appear corrupted on probe, so
there is no extra benefit in always executing the write.

The comparison to determine whether the state should be dirtied
does an extra allocation in interest of clarity.
This overhead is deemed negligible compared to I/O and it makes
the code easier to follow.

Suggested-by: Jan Lübbe <jlu@pengutronix.de>
Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Message-Id: <20201113190856.3197-1-a.fatoum@pengutronix.de>
Signed-off-by: Roland Hieber <rhi@pengutronix.de>

1 files changed, 9 insertions, 0 deletions

diff --git a/src/barebox-state.c b/src/barebox-state.c
index 7ac90c6..afd18c6 100644
--- a/src/barebox-state.c
+++ b/src/barebox-state.c
@@ -283,6 +283,7 @@ static int state_set_var(struct state *state, const char *var, const char *val)
 {
 	struct state_variable *sv;
 	struct variable_str_type *vtype;
+	char *oldval;
 	int ret;
 
 	sv = state_find_var(state, var);
@@ -296,6 +297,14 @@ static int state_set_var(struct state *state, const char *var, const char *val)
 	if (!vtype->set)
 		return -EPERM;
 
+	oldval = vtype->get(sv);
+	if (!IS_ERR(oldval)) {
+		bool equal = strcmp(oldval, val) == 0;
+		free(oldval);
+		if (equal)
+			return 0;
+	}
+
 	ret = vtype->set(sv, val);
 	if (ret)
 		return ret;