Avoid error message during a scan of a static /dev directory

Hi all,

as highlighted by Helmut (see "Re: btrfs still looks for not existing devices"), some btrfs tools (like mkfs.btrfs, btrfsck, btrfs-image, btrfs- label...) have the habit to scan the /dev directories looking for a valid block device in order to assemble all the devices of a btrfs filesystems.

Some systems doesn't use udev, so they have a static /dev with a lot of block device nodes without a real device. Another source of error is that some devices return ENOMEDIUM (No medium found) when they haven't a medium (think about a CD with the tray empty, or a SD/CF reader). These two kind of errors are reported by these tools.

I think that it is perfectly safe to ignore these error because the fact that a device doesn't exist or a CD is empty is not an error which should be handled and/or reported when the system is trying to assemble the devices for a filesystem.

In any case if a device *needed* for a btrfs filesystem is missing, an error is raised.

The patch enclosed allow to ignore the errors:
- ENXIO (device don't exists)
- ENOMEDIUM (No medium found)

avoiding spurious messages during a scanning of the /dev directory.

I have to highlight that if a CDROM/DVD is inserted, the btrfs tools read the cdrom, and this is a very slow operation.

Hugo, Chris,
please apply.

Anyway comments are welcome.

BR

P.S.
you can pull this patch from the following repository:

http://cassiopea.homelinux.net/git/btrfs-progs-unstable.git

branch

skip-not-existent-devices

gpg key@ keyserver.linux.it: Goffredo Baroncelli (ghigo) <[email protected]>
Key fingerprint = 4769 7E51 5293 D36C 814E  C054 BF04 F161 3DC5 0512

commit 3635fcf3f7358f006a5025b9773034088bdd01fd

Author: Goffredo Baroncelli <[email protected]>
Date:   Fri Oct 21 19:00:28 2011 +0200

Ignore the error ENXIO and ENOMEDIUM during a devs scan

Ignore the error ENXIO (device don't exists) and ENOMEDIUM ( No medium found -> like a cd tray empty) in the function btrfs_scan_one_dir.
This avoids spurios errors due to an empty CD or a block device node without a device (which is frequent in a static /dev).

index 86c643c..5761e47 100644
@@ -997,8 +997,14 @@ again:
 		}
 		fd = open(fullpath, O_RDONLY);
 		if (fd < 0) {
-			fprintf(stderr, "failed to read %s: %s\n", fullpath,
-					strerror(errno));
+			/* ignore the following errors:
+				ENXIO (device don't exists) 
+				ENOMEDIUM (No medium found -> 
+					like a cd tray empty)
+			*/
+			if(errno != ENXIO && errno != ENOMEDIUM) 
+				fprintf(stderr, "failed to read %s: %s\n", 
+					fullpath, strerror(errno));
 			continue;
 		}
 		ret = btrfs_scan_one_device(fd, fullpath, &tmp_devices,