From d175d6d2260cd4b2116669953058fa9bef7ae478 Mon Sep 17 00:00:00 2001
From: Lennart Poettering <lennart@poettering.net>
Date: Sun, 16 Oct 2022 22:39:31 +0200
Subject: [PATCH] generator: teach generator_add_symlink() to instantiate
 specified unit

if we want generators to instantiate a template service, we need to
teach generator_add_symlink() the concept.

Just some preparation for a later commit.

While we are at it, modernize the function around
path_extract_filename() + path_extract_directory()

(cherry picked from commit 0ba07f907721941f611eaca9521937c467bdfff2)

Related: #2190226
---
 src/shared/generator.c | 51 ++++++++++++++++++++++++++++++++++--------
 src/shared/generator.h |  6 ++++-
 2 files changed, 47 insertions(+), 10 deletions(-)

diff --git a/src/shared/generator.c b/src/shared/generator.c
index 4c684fc3e7..6001b2778c 100644
--- a/src/shared/generator.c
+++ b/src/shared/generator.c
@@ -59,19 +59,52 @@ int generator_open_unit_file(
         return 0;
 }
 
-int generator_add_symlink(const char *dir, const char *dst, const char *dep_type, const char *src) {
-        /* Adds a symlink from <dst>.<dep_type>/ to <src> (if src is absolute)
-         * or ../<src> (otherwise). */
+int generator_add_symlink_full(
+                const char *dir,
+                const char *dst,
+                const char *dep_type,
+                const char *src,
+                const char *instance) {
+
+        _cleanup_free_ char *dn = NULL, *fn = NULL, *instantiated = NULL, *to = NULL, *from = NULL;
+        int r;
+
+        assert(dir);
+        assert(dst);
+        assert(dep_type);
+        assert(src);
+
+        /* Adds a symlink from <dst>.<dep_type>/ to <src> (if src is absolute) or ../<src> (otherwise). If
+         * <instance> is specified, then <src> must be a template unit name, and we'll instantiate it. */
 
-        const char *from, *to;
+        r = path_extract_directory(src, &dn);
+        if (r < 0 && r != -EDESTADDRREQ) /* EDESTADDRREQ → just a file name was passed */
+                return log_error_errno(r, "Failed to extract directory name from '%s': %m", src);
 
-        from = path_is_absolute(src) ? src : strjoina("../", src);
-        to = strjoina(dir, "/", dst, ".", dep_type, "/", basename(src));
+        r = path_extract_filename(src, &fn);
+        if (r < 0)
+                return log_error_errno(r, "Failed to extract file name from '%s': %m", src);
+        if (r == O_DIRECTORY)
+                return log_error_errno(SYNTHETIC_ERRNO(EISDIR), "Expected path to regular file name, but got '%s', refusing.", src);
+
+        if (instance) {
+                r = unit_name_replace_instance(fn, instance, &instantiated);
+                if (r < 0)
+                        return log_error_errno(r, "Failed to instantiate '%s' for '%s': %m", fn, instance);
+        }
+
+        from = path_join(dn ?: "..", fn);
+        if (!from)
+                return log_oom();
+
+        to = strjoin(dir, "/", dst, ".", dep_type, "/", instantiated ?: fn);
+        if (!to)
+                return log_oom();
 
         (void) mkdir_parents_label(to, 0755);
-        if (symlink(from, to) < 0)
-                if (errno != EEXIST)
-                        return log_error_errno(errno, "Failed to create symlink \"%s\": %m", to);
+
+        if (symlink(from, to) < 0 && errno != EEXIST)
+                return log_error_errno(errno, "Failed to create symlink \"%s\": %m", to);
 
         return 0;
 }
diff --git a/src/shared/generator.h b/src/shared/generator.h
index 1b4f36ac53..a4049dbd8f 100644
--- a/src/shared/generator.h
+++ b/src/shared/generator.h
@@ -12,7 +12,11 @@ int generator_open_unit_file(
         const char *name,
         FILE **file);
 
-int generator_add_symlink(const char *dir, const char *dst, const char *dep_type, const char *src);
+int generator_add_symlink_full(const char *dir, const char *dst, const char *dep_type, const char *src, const char *instance);
+
+static inline int generator_add_symlink(const char *dir, const char *dst, const char *dep_type, const char *src) {
+        return generator_add_symlink_full(dir, dst, dep_type, src, NULL);
+}
 
 int generator_write_fsck_deps(
         FILE *f,