Clarification on /etc/udev/rules.d processing

Clarification on /etc/udev/rules.d processing

[Kevin P. Fleming]

I've just started using udev, and I've decided I'd much rather have 
individual config files for various purposes in /etc/udev/rules.d rather 
than one combined file.

 From my reading of the code, it appears that udev always reads all the 
files in that directory (which is good), and they are read in readdir() 
order which should mean I can control the order by using alphanumeric 
sorting of the names (also good).

What I'm not clear on is how udev will handle multiple rules that match 
for a given device: if more than one rule wants to provide a device 
name, I presume udev will stop looking for device name rules as soon as 
any rules matches, right? In spite of that, rules that add symlinks to a 
device seem to always be processed even if they appear in the file after 
the rule that supplied the device name. I think this is the correct 
behavior, but I want to make sure it's the _expected_ behavior, not just
"unspecified behavior" that could change at any time.


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Re: Clarification on /etc/udev/rules.d processing

[Kay Sievers]

On Tue, Apr 20, 2004 at 08:59:03PM -0700, Kevin P. Fleming wrote:
> I've just started using udev, and I've decided I'd much rather have 
> individual config files for various purposes in /etc/udev/rules.d rather 
> than one combined file.
> 
> From my reading of the code, it appears that udev always reads all the 
> files in that directory (which is good), and they are read in readdir() 
> order which should mean I can control the order by using alphanumeric 
> sorting of the names (also good).
> 
> What I'm not clear on is how udev will handle multiple rules that match 
> for a given device: if more than one rule wants to provide a device 
> name, I presume udev will stop looking for device name rules as soon as 
> any rules matches, right?

Yes.

> In spite of that, rules that add symlinks to a 
> device seem to always be processed even if they appear in the file after 
> the rule that supplied the device name.

No, if NAME is set by a rule, the processing is stopped. No later
"symlink only" rule will be applied.

thanks,
Kay


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Re: Clarification on /etc/udev/rules.d processing

[Kevin P. Fleming]

Kay Sievers wrote:

> No, if NAME is set by a rule, the processing is stopped. No later
> "symlink only" rule will be applied.

Any chance that behavior could be changed? For example, the current udev 
default rules file creates

/dev/device-mapper

for the device mapper control device. However, the recent standard 
location for that is

/dev/mapper/control

It is simple enough to create a SYMLINK rule to create this node, and it 
works fine. However, when using multiple rules files (in 
/etc/udev/rules.d), I'll have to ensure that the file containing my 
SYMLINK rule always gets processed before the one containing the NAME 
rule. I can do that, but it seems an unnecessary restriction.


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Re: Clarification on /etc/udev/rules.d processing

[Marco d'Itri]

On Apr 21, "Kevin P. Fleming" <kpfleming@backtobasicsmgmt.com> wrote:

> /etc/udev/rules.d), I'll have to ensure that the file containing my 
> SYMLINK rule always gets processed before the one containing the NAME 
> rule. I can do that, but it seems an unnecessary restriction.
Agreed, this is very annoying.

-- 
ciao, |
Marco | [5877 sev.CLHBjFpPY]


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