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 <[email protected]>
---
 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


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