Messages in this thread | | | Date | Fri, 30 Jan 2015 18:30:14 +0100 | From | Wouter Verhelst <> | Subject | Re: [Nbd] [RFC 4/4] nbd: Add support for nbd as root device |
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On Fri, Jan 30, 2015 at 09:04:00AM +0100, Markus Pargmann wrote: > Hi, > > On Fri, Jan 30, 2015 at 12:42:54AM +0100, Wouter Verhelst wrote: > > Not that I'm opposed to this, but you do realize that doing nbd-client > > from initramfs or similar is possible, right? Most initramfs > > implementations these days support it. > > Yes, that was the first idea how to implement a complete netboot for an > embedded ARM device. However, an initramfs is at least around 1MB in > size which has to be loaded using tftp. As the essential nbd-client > connection setup and negotiation is quite small I decided to go with > nbd-root support. > > Also it is quite useful to have nbd-root support much like nfsroot > directly built-in for debugging purposes. It has the big advantage of > booting/testing read-only filesystem images for embedded systems without > the need for an initramfs.
Fair enough, just thought I'd point it out.
When looking at your patch set, two things pop out which you should probably look at: - What will happen if someone boots with root-on-NBD in your scheme and later does a pivot_root() followed by an NBD_DISCONNECT ioctl on the device? - When a connection is started by nbd-client, the kernel creates a "pid" file in sysfs, which contains the PID of the client and which the client (when called with -c, or in other cases) uses to verify whether a device is connected. At first glance, your patch does not do this, which could cause confusion.
I must admit I haven't checked your patch very well (my kernel fu isn't that advanced) so I might have missed something, but I'd rather point it out now than have to fix the pieces afterwards ;-)
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