rm-rf: optionally rewind right before the rm_rf() operation

The comments in rm-rf.h suggested to do this already manually. Let's add
a way to make this less manual.

Author: poettering

src/shared/copy.c

@@ -710,10 +710,7 @@ static void hardlink_context_destroy(HardlinkContext *c) {
 
         if (c->dir_fd >= 0) {
                 /* <dir_fd> might be have already been used for reading, so we need to rewind it. */
-                if (lseek(c->dir_fd, 0, SEEK_SET) < 0)
-                        log_debug_errno(errno, "Failed to lseek on file descriptor, ignoring: %m");
-
-                r = rm_rf_children(TAKE_FD(c->dir_fd), REMOVE_PHYSICAL, NULL); /* consumes dir_fd in all cases, even on failure */
+                r = rm_rf_children(TAKE_FD(c->dir_fd), REMOVE_PHYSICAL|REMOVE_REWIND, NULL); /* consumes dir_fd in all cases, even on failure */
                 if (r < 0)
                         log_debug_errno(r, "Failed to remove hardlink store (%s) contents, ignoring: %m", c->subdir);
 

src/shared/rm-rf.c

@@ -308,6 +308,18 @@ static int rm_rf_children_impl(
         /* Return the first error we run into, but nevertheless try to go on.
          * The passed fd is closed in all cases, including on failure. */
 
+        assert(fd >= 0);
+
+        if (FLAGS_SET(flags, REMOVE_REWIND)) {
+                if (lseek(fd, 0, SEEK_SET) < 0) {
+                        r = -errno;
+                        safe_close(fd); /* always close */
+                        return r;
+                }
+
+                flags &= ~REMOVE_REWIND;
+        }
+
         for (;;) {  /* This loop corresponds to the directory nesting level. */
                 _cleanup_closedir_ DIR *d = NULL;
 
@@ -375,7 +387,7 @@ static int rm_rf_children_impl(
 
                         is_dir = de->d_type == DT_UNKNOWN ? -1 : de->d_type == DT_DIR;
 
-                        r = rm_rf_inner_child(fd, de->d_name, is_dir, flags, root_dev, false);
+                        r = rm_rf_inner_child(fd, de->d_name, is_dir, flags, root_dev, /* allow_recursion= */ false);
                         if (r == -EISDIR) {
                                 /* Push the current working state onto the todo list */
 
@@ -521,7 +533,7 @@ int rm_rf_child(int fd, const char *name, RemoveFlags flags) {
         if (FLAGS_SET(flags, REMOVE_ONLY_DIRECTORIES|REMOVE_SUBVOLUME))
                 return -EINVAL;
 
-        return rm_rf_inner_child(fd, name, -1, flags, NULL, true);
+        return rm_rf_inner_child(fd, name, /* is_dir= */ -1, flags, /* root_dev= */ NULL, /* allow_recursion= */ true);
 }
 
 const char* rm_rf_safe(const char *p) {

src/shared/rm-rf.h

@@ -12,6 +12,7 @@ typedef enum RemoveFlags {
         REMOVE_CHMOD            = 1 << 5, /* chmod() for write access if we cannot delete or access something */
         REMOVE_CHMOD_RESTORE    = 1 << 6, /* Restore the old mode before returning */
         REMOVE_SYNCFS           = 1 << 7, /* syncfs() the root of the specified directory after removing everything in it */
+        REMOVE_REWIND           = 1 << 8, /* Rewind the directory fd before operation */
 } RemoveFlags;
 
 int unlinkat_harder(int dfd, const char *filename, int unlink_flags, RemoveFlags remove_flags);