copy: don't synthesize a 'user.crtime_usec' xattr on copy unless explicitly requested

Previously, when we'd copy an individual file we'd synthesize a
user.crtime_usec xattr with the source's creation time if we can
determine it. As the creation/birth time was until recently not
queriable form userspace this effectively just propagated the same xattr
on the source to the same xattr on the destination. However, current
kernels now allow to query the birthtime using statx() and we do make
use of that now. Which means that suddenly we started synthesizing these
xattrs much more regularly.

Doing this actually does make sense, but only in very few cases:
not for the typical regular files we copy, but certainly when dealing
with disk images. Hence, let's keep this kind of propagation, but let's
make it a flag and default to off. Then turn it on whenever we deal with
disk images, and leave it off otherwise.

This is particularly relevant as overlayfs combining a real fs, and a
tmpfs on top will result in EOPNOTSUPP when it is attempted to open a
file with xattrs for writing, as tmpfs does not support xattrs, and
hence the copy-up cannot work. Hence, let's avoid synthesizing this
needlessly, to increase compat with overlayfs.

src/basic/copy.c

@@ -743,7 +743,7 @@ int copy_file_fd_full(
 
         r = copy_bytes_full(fdf, fdt, (uint64_t) -1, copy_flags, NULL, NULL, progress_bytes, userdata);
 
-        (void) copy_times(fdf, fdt);
+        (void) copy_times(fdf, fdt, copy_flags);
         (void) copy_xattr(fdf, fdt);
 
         return r;
@@ -849,10 +849,9 @@ int copy_file_atomic_full(
         return 0;
 }
 
-int copy_times(int fdf, int fdt) {
+int copy_times(int fdf, int fdt, CopyFlags flags) {
         struct timespec ut[2];
         struct stat st;
-        usec_t crtime = 0;
 
         assert(fdf >= 0);
         assert(fdt >= 0);
@@ -866,8 +865,12 @@ int copy_times(int fdf, int fdt) {
         if (futimens(fdt, ut) < 0)
                 return -errno;
 
-        if (fd_getcrtime(fdf, &crtime) >= 0)
-                (void) fd_setcrtime(fdt, crtime);
+        if (FLAGS_SET(flags, COPY_CRTIME)) {
+                usec_t crtime;
+
+                if (fd_getcrtime(fdf, &crtime) >= 0)
+                        (void) fd_setcrtime(fdt, crtime);
+        }
 
         return 0;
 }

src/basic/copy.h

@@ -14,6 +14,7 @@ typedef enum CopyFlags {
         COPY_REPLACE     = 1 << 2, /* Replace an existing file if there's one */
         COPY_SAME_MOUNT  = 1 << 3, /* Don't descend recursively into other file systems, across mount point boundaries */
         COPY_MERGE_EMPTY = 1 << 4, /* Merge an existing, empty directory with our new tree to copy */
+        COPY_CRTIME      = 1 << 5, /* Generate a user.crtime_usec xattr off the source crtime if there is one, on copying */
 } CopyFlags;
 
 typedef int (*copy_progress_bytes_t)(uint64_t n_bytes, void *userdata);
@@ -57,5 +58,5 @@ static inline int copy_bytes(int fdf, int fdt, uint64_t max_bytes, CopyFlags cop
         return copy_bytes_full(fdf, fdt, max_bytes, copy_flags, NULL, NULL, NULL, NULL);
 }
 
-int copy_times(int fdf, int fdt);
+int copy_times(int fdf, int fdt, CopyFlags flags);
 int copy_xattr(int fdf, int fdt);

src/boot/bootctl.c

@@ -436,7 +436,7 @@ static int copy_file_with_version_check(const char *from, const char *to, bool f
                 return log_error_errno(r, "Failed to copy data from \"%s\" to \"%s\": %m", from, t);
         }
 
-        (void) copy_times(fd_from, fd_to);
+        (void) copy_times(fd_from, fd_to, 0);
 
         if (fsync(fd_to) < 0) {
                 (void) unlink_noerrno(t);

src/import/export-raw.c

@@ -223,7 +223,7 @@ static int raw_export_process(RawExport *e) {
 
 finish:
         if (r >= 0) {
-                (void) copy_times(e->input_fd, e->output_fd);
+                (void) copy_times(e->input_fd, e->output_fd, COPY_CRTIME);
                 (void) copy_xattr(e->input_fd, e->output_fd);
         }
 

src/import/import-raw.c

@@ -215,7 +215,7 @@ static int raw_import_finish(RawImport *i) {
                 return r;
 
         if (S_ISREG(i->st.st_mode)) {
-                (void) copy_times(i->input_fd, i->output_fd);
+                (void) copy_times(i->input_fd, i->output_fd, COPY_CRTIME);
                 (void) copy_xattr(i->input_fd, i->output_fd);
         }
 

src/import/pull-raw.c

@@ -368,7 +368,7 @@ static int raw_pull_make_local_copy(RawPull *i) {
                 return log_error_errno(r, "Failed to make writable copy of image: %m");
         }
 
-        (void) copy_times(i->raw_job->disk_fd, dfd);
+        (void) copy_times(i->raw_job->disk_fd, dfd, COPY_CRTIME);
         (void) copy_xattr(i->raw_job->disk_fd, dfd);
 
         dfd = safe_close(dfd);

src/nspawn/nspawn.c

@@ -4400,7 +4400,7 @@ int main(int argc, char *argv[]) {
                                 goto finish;
                         }
 
-                        r = copy_file(arg_image, np, O_EXCL, arg_read_only ? 0400 : 0600, FS_NOCOW_FL, COPY_REFLINK);
+                        r = copy_file(arg_image, np, O_EXCL, arg_read_only ? 0400 : 0600, FS_NOCOW_FL, COPY_REFLINK|COPY_CRTIME);
                         if (r < 0) {
                                 r = log_error_errno(r, "Failed to copy image file: %m");
                                 goto finish;

src/shared/machine-image.c

@@ -870,7 +870,7 @@ int image_clone(Image *i, const char *new_name, bool read_only) {
         case IMAGE_RAW:
                 new_path = strjoina("/var/lib/machines/", new_name, ".raw");
 
-                r = copy_file_atomic(i->path, new_path, read_only ? 0444 : 0644, FS_NOCOW_FL, COPY_REFLINK);
+                r = copy_file_atomic(i->path, new_path, read_only ? 0444 : 0644, FS_NOCOW_FL, COPY_REFLINK|COPY_CRTIME);
                 break;
 
         case IMAGE_BLOCK: