linux-kernel - Re: [PATCH 1/3] mm/sparse: Clean up the obsolete code comment

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Date:   Wed, 20 Mar 2019 14:36:58 +0200
From:   Mike Rapoport <rppt@...ux.ibm.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Oscar Salvador <osalvador@...e.de>, Baoquan He <bhe@...hat.com>,
        linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
        pasha.tatashin@...cle.com, mhocko@...e.com,
        rppt@...ux.vnet.ibm.com, richard.weiyang@...il.com,
        linux-mm@...ck.org
Subject: Re: [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.

There are more than a thousand -EEXIST in the kernel, I really doubt all of
them mean "File exists" ;-)

-- 
Sincerely yours,
Mike.