[PATCH 1/2] fs: introduce unsetenv() to prepare for changing setenv(var, "") behavior

[Ahmad Fatoum]

Currently, we treat setenv(var, "") and setenv(var, NULL) the same
and delete var, which is surprising and leads to subtle quirks:

 - setenv(var, "") is specified by POSIX to set var to an empty string,
   but barebox uses it to delete variables

 - nv.user= calls nv_set with NULL parameter, but nv user="" doesn't

Make the API more POSIX-like by providing unsetenv with the expected
semantics. Most user code can then use unsetenv without worrying about
whether "" or NULL is the magic deletion value.

Signed-off-by: Ahmad Fatoum <a.fatoum at pengutronix.de>
---
 commands/readlink.c   | 2 +-
 commands/setenv.c     | 7 ++++++-
 fs/fs.c               | 2 +-
 include/environment.h | 5 +++++
 net/ifup.c            | 2 +-
 5 files changed, 14 insertions(+), 4 deletions(-)

diff --git a/commands/readlink.c b/commands/readlink.c
index fdcf175f56bb..81ad25c733ab 100644
--- a/commands/readlink.c
+++ b/commands/readlink.c
@@ -50,7 +50,7 @@ static int do_readlink(int argc, char *argv[])
 
 	return 0;
 err:
-	setenv(argv[optind + 1], "");
+	unsetenv(argv[optind + 1]);
 	return 1;
 }
 
diff --git a/commands/setenv.c b/commands/setenv.c
index ad2677065552..6992f604f513 100644
--- a/commands/setenv.c
+++ b/commands/setenv.c
@@ -10,6 +10,7 @@
 static int do_setenv(int argc, char *argv[])
 {
 	char *equal;
+	int ret;
 
 	if (argc < 2)
 		return COMMAND_ERROR_USAGE;
@@ -21,8 +22,12 @@ static int do_setenv(int argc, char *argv[])
 			argv[2] = &equal[1];
 	}
 
+	if (argv[2])
+		ret = setenv(argv[1], argv[2]);
+	else
+		ret = unsetenv(argv[1]);
 
-	return setenv(argv[1], argv[2]) ? COMMAND_ERROR : COMMAND_SUCCESS;
+	return ret ? COMMAND_ERROR : COMMAND_SUCCESS;
 }
 
 BAREBOX_CMD_HELP_START(setenv)
diff --git a/fs/fs.c b/fs/fs.c
index f41e4b9b72cd..00b8645fb0e9 100644
--- a/fs/fs.c
+++ b/fs/fs.c
@@ -3066,7 +3066,7 @@ static int automount_mount(struct dentry *dentry)
 		setenv("automount_path", am->path);
 		export("automount_path");
 		ret = run_command(am->cmd);
-		setenv("automount_path", NULL);
+		unsetenv("automount_path");
 
 		if (ret) {
 			printf("running automount command '%s' failed\n",
diff --git a/include/environment.h b/include/environment.h
index 9488e4e1ac1f..19e522cfb6b4 100644
--- a/include/environment.h
+++ b/include/environment.h
@@ -87,6 +87,11 @@ int env_push_context(void);
 
 int export(const char *);
 
+static inline int unsetenv(const char *var)
+{
+	return setenv(var, NULL);
+}
+
 #endif	/* _ENVIRONMENT_H_ */
 
 /**
diff --git a/net/ifup.c b/net/ifup.c
index a74037939b8a..1870f7401714 100644
--- a/net/ifup.c
+++ b/net/ifup.c
@@ -86,7 +86,7 @@ static int source_env_network(struct eth_device *edev)
 	env_push_context();
 
 	for (i = 0; i < ARRAY_SIZE(vars); i++)
-		setenv(vars[i], "");
+		unsetenv(vars[i]);
 
 	cmd = basprintf("source /env/network/%s", edev->devname);
 	ret = run_command(cmd);
-- 
2.28.0