Merge pull request #6922 from poettering/symlink-sockets

Fixes for Symlinks= handling in socket units

man/systemd.socket.xml

@@ -804,14 +804,13 @@
 
       <varlistentry>
         <term><varname>Symlinks=</varname></term>
-        <listitem><para>Takes a list of file system paths. The
-        specified paths will be created as symlinks to the AF_UNIX
-        socket path or FIFO path of this socket unit. If this setting
-        is used, only one AF_UNIX socket in the file system or one
-        FIFO may be configured for the socket unit. Use this option to
-        manage one or more symlinked alias names for a socket, binding
-        their lifecycle together. If the empty string is assigned, the
-        list of paths is reset. Defaults to the empty list.</para></listitem>
+        <listitem><para>Takes a list of file system paths. The specified paths will be created as symlinks to the
+        <constant>AF_UNIX</constant> socket path or FIFO path of this socket unit. If this setting is used, only one
+        <constant>AF_UNIX</constant> socket in the file system or one FIFO may be configured for the socket unit. Use
+        this option to manage one or more symlinked alias names for a socket, binding their lifecycle together. Note
+        that if creation of a symlink fails this is not considered fatal for the socket unit, and the socket unit may
+        still start. If an empty string is assigned, the list of paths is reset. Defaults to an empty
+        list.</para></listitem>
       </varlistentry>
 
       <varlistentry>

src/basic/fs-util.c

@@ -359,22 +359,25 @@ int touch(const char *path) {
 }
 
 int symlink_idempotent(const char *from, const char *to) {
-        _cleanup_free_ char *p = NULL;
         int r;
 
         assert(from);
         assert(to);
 
         if (symlink(from, to) < 0) {
+                _cleanup_free_ char *p = NULL;
+
                 if (errno != EEXIST)
                         return -errno;
 
                 r = readlink_malloc(to, &p);
-                if (r < 0)
+                if (r == -EINVAL) /* Not a symlink? In that case return the original error we encountered: -EEXIST */
+                        return -EEXIST;
+                if (r < 0) /* Any other error? In that case propagate it as is */
                         return r;
 
-                if (!streq(p, from))
-                        return -EINVAL;
+                if (!streq(p, from)) /* Not the symlink we want it to be? In that case, propagate the original -EEXIST */
+                        return -EEXIST;
         }
 
         return 0;

src/core/socket.c

@@ -38,6 +38,7 @@
 #include "exit-status.h"
 #include "fd-util.h"
 #include "format-util.h"
+#include "fs-util.h"
 #include "in-addr-util.h"
 #include "io-util.h"
 #include "label.h"
@@ -1174,7 +1175,7 @@ static int fifo_address_create(
 
         assert(path);
 
-        mkdir_parents_label(path, directory_mode);
+        (void) mkdir_parents_label(path, directory_mode);
 
         r = mac_selinux_create_file_prepare(path, S_IFIFO);
         if (r < 0)
@@ -1324,6 +1325,7 @@ static int mq_address_create(
 static int socket_symlink(Socket *s) {
         const char *p;
         char **i;
+        int r;
 
         assert(s);
 
@@ -1331,8 +1333,23 @@ static int socket_symlink(Socket *s) {
         if (!p)
                 return 0;
 
-        STRV_FOREACH(i, s->symlinks)
-                symlink_label(p, *i);
+        STRV_FOREACH(i, s->symlinks) {
+                (void) mkdir_parents_label(*i, s->directory_mode);
+
+                r = symlink_idempotent(p, *i);
+
+                if (r == -EEXIST && s->remove_on_stop) {
+                        /* If there's already something where we want to create the symlink, and the destructive
+                         * RemoveOnStop= mode is set, then we might as well try to remove what already exists and try
+                         * again. */
+
+                        if (unlink(*i) >= 0)
+                                r = symlink_idempotent(p, *i);
+                }
+
+                if (r < 0)
+                        log_unit_warning_errno(UNIT(s), r, "Failed to create symlink %s → %s, ignoring: %m", p, *i);
+        }
 
         return 0;
 }