alternatives: special-case busybox as alternatives provider

Almost all busybox applets are alternatives to some other existing
"full" utilities.  To lift the maintenance burden of enumerating CONFIG
symbols, symlink path of each applet, we special case busybox here as a
known alternatives provider.

All file pathes provided by busybox will serve as fallback alternatives
with -inf priority.  Packages intending to switch to using alternatives
mechanism will also not need to depend on the same kind of change be
applied on busybox in base system

v3 <- v2 continue to next when fetching provider pkg failed
v2 <- v1 Move busybox-specific part into data section

Signed-off-by: Yousong Zhou <zhouyousong@yunionyun.com>
Acked-by: Jo-Philipp Wich <jo@mein.io>

1 files changed, 46 insertions, 3 deletions

diff --git a/libopkg/pkg_alternatives.c b/libopkg/pkg_alternatives.c
index 50e9d12..5891616 100644
--- a/libopkg/pkg_alternatives.c
+++ b/libopkg/pkg_alternatives.c
@@ -27,6 +27,42 @@
 #include "pkg_alternatives.h"
 #include "sprintf_alloc.h"
 
+struct alternative_provider {
+	char *name;
+	char *altpath;
+};
+
+static const struct alternative_provider const providers[] = {
+	{
+		.name = "busybox",
+		.altpath = "/bin/busybox",
+	},
+};
+
+static const char *pkg_alternatives_check_providers(const char *path)
+{
+	pkg_t *pkg;
+	str_list_t *files;
+	str_list_elt_t *iter;
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(providers); i++) {
+		pkg = pkg_hash_fetch_installed_by_name(providers[i].name);
+		if (!pkg) {
+			continue;
+		}
+		files = pkg_get_installed_files(pkg);
+		for (iter = str_list_first(files); iter; iter = str_list_next(files, iter)) {
+			if (!strcmp(path, (char *)(iter->data))) {
+				pkg_free_installed_files(pkg);
+				return providers[i].altpath;
+			}
+		}
+		pkg_free_installed_files(pkg);
+	}
+	return NULL;
+}
+
 static int pkg_alternatives_update_path(pkg_t *pkg, const pkg_vec_t *installed, const char *path)
 {
 	struct pkg_alternatives *pkg_alts;
@@ -35,6 +71,7 @@ static int pkg_alternatives_update_path(pkg_t *pkg, const pkg_vec_t *installed,
 	int i, j;
 	int r;
 	char *path_in_dest;
+	const char *target_path = NULL;
 
 	for (i = 0; i < installed->len; i++) {
 		pkg_t *pkg = installed->pkgs[i];
@@ -60,6 +97,12 @@ static int pkg_alternatives_update_path(pkg_t *pkg, const pkg_vec_t *installed,
 		return -1;
 
 	if (the_alt) {
+		target_path = the_alt->altpath;
+	} else {
+		target_path = pkg_alternatives_check_providers(path);
+	}
+
+	if (target_path) {
 		struct stat sb;
 
 		r = lstat(path_in_dest, &sb);
@@ -72,7 +115,7 @@ static int pkg_alternatives_update_path(pkg_t *pkg, const pkg_vec_t *installed,
 				goto out;
 			}
 			realpath = xreadlink(path_in_dest);
-			if (realpath && strcmp(realpath, the_alt->altpath))
+			if (realpath && strcmp(realpath, target_path))
 				unlink(path_in_dest);
 			free(realpath);
 		} else if (errno != ENOENT) {
@@ -87,7 +130,7 @@ static int pkg_alternatives_update_path(pkg_t *pkg, const pkg_vec_t *installed,
 			if (r) {
 				goto out;
 			}
-			r = symlink(the_alt->altpath, path_in_dest);
+			r = symlink(target_path, path_in_dest);
 			if (r && errno == EEXIST) {
 				/*
 				 * the strcmp & unlink check above will make sure that if EEXIST
@@ -96,7 +139,7 @@ static int pkg_alternatives_update_path(pkg_t *pkg, const pkg_vec_t *installed,
 				r = 0;
 			}
 			if (r) {
-				opkg_perror(ERROR, "failed symlinking %s -> %s", path_in_dest, the_alt->altpath);
+				opkg_perror(ERROR, "failed symlinking %s -> %s", path_in_dest, target_path);
 			}
 		}
 	} else {