Messages in this thread | | | Date | Mon, 11 Dec 2006 00:23:16 +0100 | From | Pavel Machek <> | Subject | Re: [PATCH] nbd: show nbd client pid in sysfs |
| |
On Mon 2006-12-11 00:18:01, Wouter Verhelst wrote: > On Sun, Dec 10, 2006 at 08:58:19PM +0100, Pavel Machek wrote: > > Hi! > > Hi > > > > > > This simple patch allows nbd to expose the nbd-client > > > > > daemon's PID in /sys/block/nbd<x>/pid. This is helpful > > > > > for tracking connection status of a device and for > > > > > determining which nbd devices are currently in use. > > > > > > > > Actually is it needed at all? Perhaps nbd clients should be modified > > > > to put nbdX in their process nam? > > > > > > I don't think that's the right approach; only the kernel can guarantee > > > that a given process is actually managing a given nbd device (I could > > > have some rogue process running around announcing that it's managing > > > nbd2, and then what?) > > > > I'd say "do not run rogue processes as root" :-). > > > > nbd-client should run as root -- I do not think interface was > > carefully audited to run it as a user -- so rogue process should not > > really be a problem. > > IOW, you're suggesting I walk the process list from userspace to find a > process for which a) it claims it's running for a given nbd device, and > b) I can verify that it actually has the permissions to do so. That's a > whole lot of code in comparison to > > f=open("/sys/block/nbd2/pid", O_RDONLY); > read(f,buf,len); > > I think I very much prefer the above two lines, not only for simplicity. > > Also, your suggestion relies on users /only/ using the official > nbd-client, and is fragile in cases where that assumption is false > (i.e., it's susceptible to false negatives). The suggested patch does > not have that problem.
I do not think finding out "which pid is controlling nbd#2" is _that_ important.
We have /var/lock files for ttyS*, I do not see reason why nbd should be different. Actually you could copy /var/lock approach.
And BTW that /sys/ thingie is racy by design (as is the log file). By the time you try to do anything with that PID, process may be gone. Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |