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SubjectRe: [PATCH 1/3] mm/sparse: Clean up the obsolete code comment
On Wed, Mar 20, 2019 at 05:22:43AM -0700, Matthew Wilcox wrote:
> On Wed, Mar 20, 2019 at 01:20:15PM +0100, Oscar Salvador wrote:
> > On Wed, Mar 20, 2019 at 04:19:59AM -0700, Matthew Wilcox wrote:
> > > On Wed, Mar 20, 2019 at 03:35:38PM +0800, Baoquan He wrote:
> > > > /*
> > > > - * returns the number of sections whose mem_maps were properly
> > > > - * set. If this is <=0, then that means that the passed-in
> > > > - * map was not consumed and must be freed.
> > > > + * sparse_add_one_section - add a memory section
> > > > + * @nid: The node to add section on
> > > > + * @start_pfn: start pfn of the memory range
> > > > + * @altmap: device page map
> > > > + *
> > > > + * Return 0 on success and an appropriate error code otherwise.
> > > > */
> > >
> > > I think it's worth documenting what those error codes are. Seems to be
> > > just -ENOMEM and -EEXIST, but it'd be nice for users to know what they
> > > can expect under which circumstances.
> > >
> > > Also, -EEXIST is a bad errno to return here:
> > >
> > > $ errno EEXIST
> > > EEXIST 17 File exists
> > >
> > > What file? I think we should be using -EBUSY instead in case this errno
> > > makes it back to userspace:
> > >
> > > $ errno EBUSY
> > > EBUSY 16 Device or resource busy
> >
> > We return -EEXIST in case the section we are trying to add is already
> > there, and that error is being caught by __add_pages(), which ignores the
> > error in case is -EXIST and keeps going with further sections.
> >
> > Sure we can change that for -EBUSY, but I think -EEXIST makes more sense,
> > plus that kind of error is never handed back to userspace.
>
> Not returned to userspace today. It's also bad precedent for other parts
> of the kernel where errnos do get returned to userspace.

Yes, I get your point, but I do not really see -EBUSY fitting here.
Actually, we do have the same kind of situation when dealing with resources.
We return -EEXIST in register_memory_resource() in case the resource we are
trying to add conflicts with another one.

I think that -EEXIST is more intuitive in that code path, but I am not going to
insist.

--
Oscar Salvador
SUSE L3

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