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DaggyStyle
Watchman
Joined: 22 Mar 2006
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 Posted: Sat Mar 20, 2021 4:18 pm Post subject: cmd line vs /etc/modprobe.d precedence |
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Greetings,
I'm trying to determine precedence of setting module's option via cmd line or /etc/modprobe.d but I'm unable to find info regarding it.
my assumption is that incase it isn't build-in /etc/modprobe.d takes precedence.
anyone knows?
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NeddySeagoon
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Joined: 05 Jul 2003
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| Posted: Sat Mar 20, 2021 8:50 pm Post subject: |
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DaggyStyle,
/etc/modprobe.d is processed by the modules service which is in the boot runlevel.
That means its done its stuff before you can log in.
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Computer users fall into two groups:-
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Goverp
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Joined: 07 Mar 2007
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| Posted: Sun Mar 21, 2021 10:41 am Post subject: |
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Neddy, IIUC that might be the right answer to the wrong question! Depends on which cmd line DaggyStyle is talking about.
Reading the kernel docs on the command line (which I assume is what DaggyStyle is asking about), it says
| Quote: | | Parameters for modules which are built into the kernel need to be specified on the kernel command line. modprobe looks through the kernel command line (/proc/cmdline) and collects module parameters when it loads a module, so the kernel command line can be used for loadable modules too. |
I'd hope that overrode modprobe.d, not least because it should happen to modules loaded before the kernel can even access modprobe.d! And surely the purpose of command line overrides is to, ahem, override.
Of course, if you mean parameters on a terminal command line, I guess you're typing "modprobe <module> <overrides>", in which case the man text doesn't say, but I'd be very unhappy if modprobe.d overrode my overrides!
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NeddySeagoon
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| Posted: Sun Mar 21, 2021 10:59 am Post subject: |
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Goverp,
Thank you. I hadn't even thought about the kernel command line.
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NeddySeagoon
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GDH-gentoo
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| Posted: Sun Mar 21, 2021 1:55 pm Post subject: |
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| Looking at libkmod's code, it seems that module options from the kernel command line are appended to those specified in /etc/modprobe.d/*.config files, so I'd expect the former to take precedence. |
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DaggyStyle
Watchman
Joined: 22 Mar 2006
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| Posted: Mon Mar 22, 2021 4:20 pm Post subject: |
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thank you all for the answers, basically what I need is the ability to override the ids option values if vfio-pci module is is loaded at later stage.
question is, will setting it in the cmdline will work?
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GDH-gentoo
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| Posted: Tue Mar 23, 2021 1:31 am Post subject: |
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| If the option is specified in the kernel command line (vfio-pci.ids=whatever), it should get passed when the module loads. |
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DaggyStyle
Watchman
Joined: 22 Mar 2006
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| Posted: Tue Mar 23, 2021 8:21 am Post subject: |
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| GDH-gentoo wrote: | | If the option is specified in the kernel command line (vfio-pci.ids=whatever), it should get passed when the module loads. |
thus overriding the entry in /etc/modprobe.d/vfio.conf?
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Goverp
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| Posted: Tue Mar 23, 2021 10:18 am Post subject: |
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Why not try it and report back?
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GDH-gentoo
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| Posted: Tue Mar 23, 2021 2:49 pm Post subject: |
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| DaggyStyle wrote: | | thus overriding the entry in /etc/modprobe.d/vfio.conf? |
If a file in /etc/modprobe.d contains:
| Code: | | options vfio-pci ids=value1 |
and this was specified in the command line:
| Code: | | vfio-pci.ids=value2 |
if I understood libkmod's code correctly, at the time of module load (by an OpenRC service calling modprobe, by the udev daemon, which also links to libkmod, etc.) the behaviour is as if this command was used:
| Code: | | modprobe vfio-pci ids=value1 ids=value2 |
What happpens when the module's code sees the same option twice depends on the module, I guess.
| Goverp wrote: | | Why not try it and report back? |
Indeed, it's the best way to now if it works  |
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DaggyStyle
Watchman
Joined: 22 Mar 2006
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| Posted: Tue Mar 23, 2021 4:40 pm Post subject: |
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| Goverp wrote: | | Why not try it and report back? |
the system in question is a production server, I cannot take it down to test
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NeddySeagoon
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| Posted: Tue Mar 23, 2021 5:03 pm Post subject: |
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DaggyStyle,
You need to test it somewhere before you deploy to production.
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NeddySeagoon
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Kernel & Hardware
