Misleading error message in btrfsctl

Misleading error message in btrfsctl

[Peter Klotz]

[-- Attachment #1: Type: text/plain, Size: 602 bytes --]

Calling btrfsctl results in this message when module btrfs.ko is not loaded:

root@asus:/root# btrfsctl -A /dev/sda
ioctl:: Bad file descriptor

An strace shows that actually opening of /dev/btrfs-control failed.

open("/dev/btrfs-control", O_RDWR)      = -1 ENOENT (No such file or 
directory)
ioctl(4294967295, 0x50009404, 0x7fff11fb76b0) = -1 EBADF (Bad file 
descriptor)

The attached patch (against btrfsctl 0.18) terminates btrfsctl if 
/dev/btrfs-control cannot be opened.

The output with applied patch:

root@asus:/root# btrfsctl -A /dev/sda
failed to open /dev/btrfs-control

Regards, Peter.

[-- Attachment #2: btrfs-control-open.patch --]
[-- Type: text/x-patch, Size: 522 bytes --]

diff -Nur btrfs-progs-0.18/btrfsctl.c btrfs-progs-0.18.patched/btrfsctl.c
--- btrfs-progs-0.18/btrfsctl.c	2009-01-17 02:08:19.000000000 +0100
+++ btrfs-progs-0.18.patched/btrfsctl.c	2009-01-18 14:16:25.000000000 +0100
@@ -189,6 +189,10 @@
 
 	if (command == BTRFS_IOC_SCAN_DEV) {
 		fd = open("/dev/btrfs-control", O_RDWR);
+		if (fd < 0) {
+                	fprintf(stderr, "failed to open /dev/btrfs-control\n");
+                       exit(1);
+	        }
 		name = fname;
 	 } else {
 		fd = open_file_or_dir(fname);

Re: Misleading error message in btrfsctl

[Calvin Walton]

On Sun, 2009-01-18 at 14:40 +0100, Peter Klotz wrote:
> Calling btrfsctl results in this message when module btrfs.ko is not loaded:
> 
> root@asus:/root# btrfsctl -A /dev/sda
> ioctl:: Bad file descriptor
..
> The output with applied patch:
> 
> root@asus:/root# btrfsctl -A /dev/sda
> failed to open /dev/btrfs-control

It would probably be better to use perror() instead of fprintf, in order
to give the actual error message. I often find it useful to know why the
device failed to open - is it missing, permission issues? I've updated
the patch:

diff --git a/btrfsctl.c b/btrfsctl.c
index e049799..df1a165 100644
--- a/btrfsctl.c
+++ b/btrfsctl.c
@@ -189,6 +189,10 @@ int main(int ac, char **av)
 
 	if (command == BTRFS_IOC_SCAN_DEV) {
 		fd = open("/dev/btrfs-control", O_RDWR);
+		if (fd < 0) {
+			perror("failed to open /dev/btrfs-control");
+			exit(1);
+		}
 		name = fname;
 	 } else {
 		fd = open_file_or_dir(fname);

-- 
Calvin Walton <calvin.walton@gmail.com>

Re: Misleading error message in btrfsctl

[Chris Mason]

On Sun, 2009-01-18 at 09:12 -0500, Calvin Walton wrote:
> On Sun, 2009-01-18 at 14:40 +0100, Peter Klotz wrote:
> > Calling btrfsctl results in this message when module btrfs.ko is not loaded:
> > 
> > root@asus:/root# btrfsctl -A /dev/sda
> > ioctl:: Bad file descriptor
> ..
> > The output with applied patch:
> > 
> > root@asus:/root# btrfsctl -A /dev/sda
> > failed to open /dev/btrfs-control
> 
> It would probably be better to use perror() instead of fprintf, in order
> to give the actual error message. I often find it useful to know why the
> device failed to open - is it missing, permission issues? I've updated
> the patch:
> 

Thanks

-chris