I'm working at a system, where a server manages multiple PCIe data acquisition cards. Each card has its individual serial number available in the extended PCIe configuration space. The cards are controlled as UIO devices. Unfortunately, it appears that the card are sometimes enumerated in the random order. Proper management of the system requires that there are symlinks created with names permanently associated with the individual
cards.
Can't you adjust the kernel configuration so that it forces
certain probes to yield certain "devices"?
E.g., instead of letting NetBSD probe disk drives in whatever order
it encounters them -- and assigning device names in that order -- I
build my kernels so certain device names are set aside for specific
devices (which may or may not be present at any given boot).
Don Y <blockedofcourse@foo.invalid> wrote:
Can't you adjust the kernel configuration so that it forces
certain probes to yield certain "devices"?
E.g., instead of letting NetBSD probe disk drives in whatever order
it encounters them -- and assigning device names in that order -- I
build my kernels so certain device names are set aside for specific
devices (which may or may not be present at any given boot).
That's what udev does. udev has a set of rules that indicate how devices should be turned into device nodes, be it by physical location (PCI slot), vendor/product ID, serial number, etc. It also sets ownership and permissions of those device nodes (so only certain users can access a
device node).
It handles creating and removing device nodes as devices are
hot plugged. It's all just some textual config files, no kernel compilation needed.
The problem in this case is that PCI devices don't as standard support a serial number in the way that USB or SATA does, and so this manufacturer has done their own thing in the way the serial number is embedded. That is why some helper code is needed to expose the serial number to udev to use in its device naming.
(although I would have expected a rule that sets up device nodes named by
PCI slot to be equally predictable)
On 5/19/2021 1:30 AM, Theo wrote:
Don Y <blocked...@foo.invalid> wrote:
Can't you adjust the kernel configuration so that it forces
certain probes to yield certain "devices"?
E.g., instead of letting NetBSD probe disk drives in whatever order
it encounters them -- and assigning device names in that order -- I
build my kernels so certain device names are set aside for specific
devices (which may or may not be present at any given boot).
That's what udev does. udev has a set of rules that indicate how devices should be turned into device nodes, be it by physical location (PCI slot), vendor/product ID, serial number, etc. It also sets ownership and permissions of those device nodes (so only certain users can access a device node).OK. In NetBSD, that's part of the kernel configuration.
Things like permissions and device types (char vs block)
are handled in reasonably static files:
---------
device-major ccd char 300 block 300 ccd
device-major vnd char 301 block 301 vnd
device-major md char 302 block 302 md
device-major ld char 303 block 303 ld
device-major raid char 304 block 304 raid
device-major cgd char 305 block 305 cgd
# scsibus and its children
device-major scsibus char 310 scsibus
device-major sd char 311 block 311 sd
device-major st char 312 block 312 st
device-major cd char 313 block 313 cd
device-major ch char 314 ch
device-major ss char 315 ss
device-major uk char 316 uk
device-major ses char 317 ses
device-major se char 318 se
device-major fd char 320 block 320 fdc
...
device-major com char 260 com
device-major lpt char 261 lpt
...
-------
while the binding of device identifiers is part of the "config"
file:
------
# SCSI devices
sd* at scsibus? target ? lun ? # SCSI disk drives
st* at scsibus? target ? lun ? # SCSI tape drives
cd* at scsibus? target ? lun ? # SCSI CD-ROM drives
ch* at scsibus? target ? lun ? # SCSI autochangers
ses* at scsibus? target ? lun ? # SCSI Enclosure Services devices
ss* at scsibus? target ? lun ? # SCSI scanners
uk* at scsibus? target ? lun ? # SCSI unknown
----
E.g., in the above, I could ensure sd3 was always a particular
device on a particular scsibus at a particular SCSI ID by
creating an entry with the various wildcards (? *) replaced
by specific values. The probe will preallocate those so
they aren't assigned to some other device that happened
to be Nth in order of detection.
It handles creating and removing device nodes as devices are
hot plugged. It's all just some textual config files, no kernel compilation
needed.
The problem in this case is that PCI devices don't as standard support a serial number in the way that USB or SATA does, and so this manufacturer hasAh. I'd have thought an alternative would just be to ensure devices
done their own thing in the way the serial number is embedded. That is why some helper code is needed to expose the serial number to udev to use in its
device naming.
of that specific *type* (manufacturer) were probed in an order that
could be enforced by the equivalent of the scheme I mentioned above.
(although I would have expected a rule that sets up device nodes named by PCI slot to be equally predictable)I guess one unanswered question is whether Wojciech is bolting his solution onto an existing system *or* designing a system from scratch (in which case, you would assume he could exercise some control over how the hardware is "built"/pieced together)
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