Re: [Xen-devel] [PATCH 3 of 4] libxl: Introduce pci_assignable_add and pci_assignable_remove

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Thu, 2012-05-10 at 17:29 +0100, George Dunlap wrote:
> On 10/05/12 16:04, Ian Campbell wrote:
> >>>> +    spath = libxl__sprintf(gc, SYSFS_PCI_DEV"/"PCI_BDF"/driver",
> >>>> +                           pcidev->domain,
> >>>> +                           pcidev->bus,
> >>>> +                           pcidev->dev,
> >>>> +                           pcidev->func);
> >>>> +    if ( !lstat(spath,&st) ) {
> >>>> +        /* Find the canonical path to the driver. */
> >>>> +        *dp = libxl__zalloc(gc, PATH_MAX);
> >>> Should we be actually using fpathconf / sysconf here?
> >> I don't really follow.  What exactly is it you're proposing?
> > PATH_MAX isn't really a constant these days, you can get the dynamic
> > value for a particular filesystem from fpathconf. I honestly don't know
> > how much of a concern this really is, especially given we are always
> > necessarily talking to sysfs.
> Ah right -- I didn't get that you were referring to PATH_MAX.  The 
> "realpath" manpage specifies:   "The resulting pathâname is stored as a 
> null-terminated string, up to a maximum of PATH_MAX bytes, in the buffer 
> pointed to by resolved_path."  That's why I used PATH_MAX in the 
> allocation.  I would hope that if the manpage says PATH_MAX, it means 
> PATH_MAX, and not "some other thing which you can get by running this 
> complicated command I haven't mentioned". :-)

Yes, that's fair ;-)

I think the issue might be that some systems declare PATH_MAX to be
enormous (to cover all bases) and sysconf lets you use something more
realistic/relevant to the actual situation.

Looks like on Linux it is 4096, which I guess is ok.

> OK -- I've also added a comment explaining why I'm doing what I'm doing 
> with slots, which I'll include when I re-post the patch.

Ta!

Ian.



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