linux-kernel - Re: [patch 1/6] mempolicy: convert MPOL constants to enum

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Message-Id: <20080225212056.ca388983.pj@sgi.com>
Date:	Mon, 25 Feb 2008 21:20:56 -0600
From:	Paul Jackson <pj@....com>
To:	David Rientjes <rientjes@...gle.com>
Cc:	akpm@...ux-foundation.org, clameter@....com,
	Lee.Schermerhorn@...com, ak@...e.de, linux-kernel@...r.kernel.org
Subject: Re: [patch 1/6] mempolicy: convert MPOL constants to enum

David wrote:

+enum {
+	MPOL_DEFAULT,
+	MPOL_PREFERRED,
+	MPOL_BIND,
+	MPOL_INTERLEAVE,
+	MPOL_MAX,	/* always last member of enum */

Aren't the values that these constants take part of the
user visible kernel API?

In other words, if someone added another MPOL_* in the middle
of this enum, it would break mbind/set_mempolicy/get_mempolicy
users, right:

+enum {
+	MPOL_DEFAULT,
+	MPOL_PREFERRED,
+	MPOL_YET_ANOTHER_FLAG,		/* <== added flag ... oops */
+	MPOL_BIND,
+	MPOL_INTERLEAVE,
+	MPOL_MAX,	/* always last member of enum */

I'm thinking that we should still specify the specific value
of each of these flags, by way of documenting these necessary
values, as in:

+enum {
+	MPOL_DEFAULT = 0,
+	MPOL_PREFERRED = 1,
+	MPOL_BIND = 2,
+	MPOL_INTERLEAVE = 3,
+	MPOL_MAX,	/* always last member of enum */


-- 
                  I won't rest till it's the best ...
                  Programmer, Linux Scalability
                  Paul Jackson <pj@....com> 1.940.382.4214
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