Re: Reason why "nocache" option is not displayed in "mount"?

[Alexander Leidinger]

Am 2024-03-09 15:27, schrieb Rick Macklem:

On Sat, Mar 9, 2024 at 5:08 AM Alexander Leidinger
<alexan...@leidinger.net> wrote:

Am 2024-03-09 06:07, schrieb Warner Losh:

> On Thu, Mar 7, 2024 at 1:05 PM Jamie Landeg-Jones <ja...@catflap.org>
> wrote:
>
>> Alexander Leidinger <alexan...@leidinger.net> wrote:
>>
>>> Hi,
>>>
>>> what is the reason why "nocache" is not displayed in the output of
>>> "mount" for nullfs options?
>>
>> Good catch. I also notice that "hidden" is not shown either.
>>
>> I guess that as for some time, "nocache" was a "secret" option, no-one
>> update "mount" to display it?
>
> So a couple of things to know.
>
> First, there's a list of known options. These are converted to a
> bitmask. This is then decoded and reported by mount. The other strings
> are passed to the filesystem directly. They decode it and do things,
> but they don't export them (that I can find). I believe that's why they
> aren't reported with 'mount'. There's a couple of other options in
> /etc/fstab that are pseudo options too.


is recorded in a nullfs private flag and that the userland can not

this and some other things).


this was lost in translation...

Regarding the issue of not being able to see all options which are in
effect for a given mount point (not specific to nocache): I consider
this to be a bug.
Pseudo options like "late" or "noauto" in fstab which don't make sense
to use when you use mount(8) a FS by hand, I do not consider here.

That's the technical explanation why it doesn't work. I'm a step further since initial mail, I even had a look at the code and know that nocache access this (mount looks at struct statfs which doesn't provide info to My question was targeted more in the direction if there is a conceptual reason or if it was an oversight that it is not displayed. I admit that

As a data point, I added the "-m"option to nfsstat(1) so that all the nfs

related options get displayed.


defers processing options to the file systems.

Part of the problem is that this will be file system specific, since nmount()

    https://cgit.freebsd.org/src/tree/sys/sys/mount.h#n515






Bye,
Alexander.

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There exists values for a lot of the mount opions which are not displayed. For example the nocache option for nullfs is MNTK_NULL_NOCACHE in This may not be useable as is, but I use it to show that there are already bits public about it, just not in the proper place to be useful to the userland. Even FS specific options could be set as part of statfs (by letting the FS set them in struct statfs). Or there could be a per-mount callback / ioctl / whatever which provides the options in some way to the userland if requested. So we either have something which could be used but requires some interface to let a FS set a value somewhere, or if this is a too gross hack, we would need to come up with a new interface to query this info.

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