Re: [PATCH 06/24] md: open code vfs_stat in md_setup_drive

On Tue, Jul 21, 2020 at 06:28:00PM +0200, Christoph Hellwig wrote:

Instead of passing a kernel pointer to vfs_stat by relying on the
implicit set_fs(KERNEL_DS) in md_setup_drive, just open code the
trivial getattr, and use the opportunity to move a little bit more
code from the caller into the new helper.

Ugh...

+static void __init md_lookup_dev(const char *devname, dev_t *dev)
+{
+	struct kstat stat;
+	struct path path;
+	char filename[64];
+
+	if (strncmp(devname, "/dev/", 5) == 0)
+		devname += 5;
+	snprintf(filename, 63, "/dev/%s", devname);
+
+	if (!kern_path(filename, LOOKUP_FOLLOW, &path) &&
+	    !vfs_getattr(&path, &stat, STATX_BASIC_STATS, AT_NO_AUTOMOUNT) &&
+	    S_ISBLK(stat.mode))
+		*dev = new_decode_dev(stat.rdev);
+	path_put(&path);
+}

How about fs/for_init.c and putting the damn helpers there?  With
calling conventions as close to syscalls as possible, and a fat
comment regarding their intended use being _ONLY_ the setup
in should-have-been-done-in-userland parts of init?

I really want to keep the surface as small as possible - we had
fun shite several releases ago when somebody tried that kind of
crap (with open(), IIRC).  Let's not go there again...