Re: [PATCH] [V2] add options to ps(1) to display lwp data

["Simon 'corecode' Schubert" <corecode@xxxxxxxxxxxx>]

Matthew Dillon wrote:
> :It wasn't ment to be a pointer, just an identifier.  And the td pointer is a perfect identifier.  Of course, it doesn't format as nicely as a small number, but so what.  pid == -1 means kernel, tid *always* means thread identifier.
> :
> :cheers
> :  simon
>
>     It can't be negative and I don't want to hack around the fact by masking
>     it with 0x7fffffff, because that requires visibility into the machine
>     layer to work properly in 64 bit environments.  Also, there's nothing
>     that says the TID is going to be the same or similar in size to a pointer,
>     and userland does in fact need the TID because that's what you specify
>     when you send signals.
>
>     We can't just use a thread pointer between userland and the kernel.
>     The kernel has to validate the ID passed to it either way so it just
>     doesn't save any work at all to do that.

We can't signal a kernel thread anyways, so this is simply just kernel->userland data export.  This is anyways only informational for ps and top and thelike, and also only if they want to show kernel threads.

By setting tid to -1 we lose information.  Of course not setting it to -1 means we need more intelligence in ps etc, but they need a certain amount of intelligence anyways.  Adding a new field means we need this intelligence *anyways* in ps, so there is no gain *at all*.

The pointer not fitting into the tid field is a valid point, however.  Still, this interface is proc and lwp centric and only as a *special case* it is being used to export kernel thread information.  So we really shouldn't add a special field for that.  Oh well, thinking of it, maybe we don't need the td ident at all :/

cheers
 simon

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