homework: allow specifying a dir component in CIFS services

Allow specifying CIFS services in the format //host/service/subdir/… to
allow multiple homedirs on the same share, and not in the main dir of
the share.

All other backends allow placing the data store at arbitrary places,
let's allow this too for the CIFS backend. This is particularly useful
for testing.

docs/USER_RECORD.md

@@ -411,7 +411,9 @@ useful when `cifs` is used as storage mechanism for the user's home directory,
 see above.
 
 `cifsService` → A string indicating the Windows File Share service (CIFS) to
-mount as home directory of the user on login.
+mount as home directory of the user on login. Should be in format
+`//<host>/<service>/<directory/…>`. The directory part is optional. If missing
+the top-level directory of the CIFS share is used.
 
 `imagePath` → A string with an absolute file system path to the file, directory
 or block device to use for storage backing the home directory. If the `luks`

man/homectl.xml

@@ -690,8 +690,11 @@
         <term><option>--cifs-service=</option><replaceable>SERVICE</replaceable></term>
 
         <listitem><para>Configures the Windows File Sharing (CIFS) domain and user to associate with the home
-        directory/user account, as well as the file share ("service") to mount as directory. The latter is used when
-        <literal>cifs</literal> storage is selected.</para></listitem>
+        directory/user account, as well as the file share ("service") to mount as directory. The latter is
+        used when <literal>cifs</literal> storage is selected. The file share should be specified in format
+        <literal>//<replaceable>host</replaceable>/<replaceable>share</replaceable>/<replaceable>directory/…</replaceable></literal>. The
+        directory part is optional — if not specified the home directory will be placed in the top-level
+        directory of the share.</para></listitem>
       </varlistentry>
 
       <varlistentry>

src/home/homework-cifs.c

@@ -7,6 +7,7 @@
 #include "fs-util.h"
 #include "homework-cifs.h"
 #include "homework-mount.h"
+#include "mkdir.h"
 #include "mount-util.h"
 #include "process-util.h"
 #include "stat-util.h"
@@ -18,6 +19,7 @@ int home_setup_cifs(
                 HomeSetupFlags flags,
                 HomeSetup *setup) {
 
+        _cleanup_free_ char *chost = NULL, *cservice = NULL, *cdir = NULL, *chost_and_service = NULL, *j = NULL;
         char **pw;
         int r;
 
@@ -38,6 +40,15 @@ int home_setup_cifs(
         if (!h->cifs_service)
                 return log_error_errno(SYNTHETIC_ERRNO(EINVAL), "User record lacks CIFS service, refusing.");
 
+        r = parse_cifs_service(h->cifs_service, &chost, &cservice, &cdir);
+        if (r < 0)
+                return log_error_errno(r, "Failed parse CIFS service specification: %m");
+
+        /* Just the host and service part, without the directory */
+        chost_and_service = strjoin("//", chost, "/", cservice);
+        if (!chost_and_service)
+                return log_oom();
+
         r = home_unshare_and_mkdir();
         if (r < 0)
                 return r;
@@ -78,7 +89,7 @@ int home_setup_cifs(
                 if (r == 0) {
                         /* Child */
                         execl("/bin/mount", "/bin/mount", "-n", "-t", "cifs",
-                              h->cifs_service, HOME_RUNTIME_WORK_DIR,
+                              chost_and_service, HOME_RUNTIME_WORK_DIR,
                               "-o", options, NULL);
 
                         log_error_errno(errno, "Failed to execute mount: %m");
@@ -104,10 +115,23 @@ int home_setup_cifs(
         if (r < 0)
                 return r;
 
-        setup->root_fd = open(HOME_RUNTIME_WORK_DIR, O_RDONLY|O_CLOEXEC|O_DIRECTORY|O_NOFOLLOW);
+        if (cdir) {
+                j = path_join(HOME_RUNTIME_WORK_DIR, cdir);
+                if (!j)
+                        return log_oom();
+
+                if (FLAGS_SET(flags, HOME_SETUP_CIFS_MKDIR)) {
+                        r = mkdir_p(j, 0700);
+                        if (r < 0)
+                                return log_error_errno(r, "Failed to create CIFS subdirectory: %m");
+                }
+        }
+
+        setup->root_fd = open(j ?: HOME_RUNTIME_WORK_DIR, O_RDONLY|O_CLOEXEC|O_DIRECTORY|O_NOFOLLOW);
         if (setup->root_fd < 0)
                 return log_error_errno(errno, "Failed to open home directory: %m");
 
+        setup->mount_suffix = TAKE_PTR(cdir);
         return 0;
 }
 
@@ -139,7 +163,7 @@ int home_activate_cifs(
 
         setup->root_fd = safe_close(setup->root_fd);
 
-        r = home_move_mount(NULL, hd);
+        r = home_move_mount(setup->mount_suffix, hd);
         if (r < 0)
                 return r;
 
@@ -171,7 +195,7 @@ int home_create_cifs(UserRecord *h, HomeSetup *setup, UserRecord **ret_home) {
                 return log_error_errno(errno, "Unable to detect whether /sbin/mount.cifs exists: %m");
         }
 
-        r = home_setup_cifs(h, 0, setup);
+        r = home_setup_cifs(h, HOME_SETUP_CIFS_MKDIR, setup);
         if (r < 0)
                 return r;
 

src/home/homework.c

@@ -365,6 +365,8 @@ int home_setup_done(HomeSetup *setup) {
         if (setup->do_drop_caches)
                 drop_caches_now();
 
+        setup->mount_suffix = mfree(setup->mount_suffix);
+
         return r;
 }
 

src/home/homework.h

@@ -37,6 +37,8 @@ typedef struct HomeSetup {
 
         uint64_t partition_offset;
         uint64_t partition_size;
+
+        char *mount_suffix;           /* The directory to use as home dir is this path below /run/systemd/user-home-mount */
 } HomeSetup;
 
 typedef struct PasswordCache {
@@ -66,6 +68,9 @@ static inline bool password_cache_contains(const PasswordCache *cache, const cha
 /* Various flags for the operation of setting up a home directory */
 typedef enum HomeSetupFlags {
         HOME_SETUP_ALREADY_ACTIVATED = 1 << 0, /* Open an already activated home, rather than activate it afresh */
+
+        /* CIFS backend: */
+        HOME_SETUP_CIFS_MKDIR        = 1 << 1, /* Create CIFS subdir when missing */
 } HomeSetupFlags;
 
 int home_setup_done(HomeSetup *setup);