linux-kernel - [tip:x86/pat] x86: Document get_user_pages

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Message-ID: <tip-a0d22f485af1553060b4094ee0154537a8f6a8a6@git.kernel.org>
Date:	Fri, 10 Apr 2009 12:33:46 GMT
From:	Andy Grover <andy.grover@...cle.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, hpa@...or.com, mingo@...hat.com,
	andy.grover@...cle.com, tglx@...utronix.de, mingo@...e.hu
Subject: [tip:x86/pat] x86: Document get_user_pages_fast()

Commit-ID:  a0d22f485af1553060b4094ee0154537a8f6a8a6
Gitweb:     http://git.kernel.org/tip/a0d22f485af1553060b4094ee0154537a8f6a8a6
Author:     Andy Grover <andy.grover@...cle.com>
AuthorDate: Thu, 9 Apr 2009 16:45:29 -0700
Committer:  Ingo Molnar <mingo@...e.hu>
CommitDate: Fri, 10 Apr 2009 13:14:08 +0200

x86: Document get_user_pages_fast()

While better than get_user_pages(), the usage of gupf(),
especially the return values and the fact that it can
potentially only partially pin the range, warranted some
documentation.

Signed-off-by: Andy Grover <andy.grover@...cle.com>
Cc: npiggin@...e.de
Cc: akpm@...ux-foundation.org
LKML-Reference: <1239320729-3262-1-git-send-email-andy.grover@...cle.com>
Signed-off-by: Ingo Molnar <mingo@...e.hu>


---
 arch/x86/mm/gup.c |   16 ++++++++++++++++
 1 files changed, 16 insertions(+), 0 deletions(-)

diff --git a/arch/x86/mm/gup.c b/arch/x86/mm/gup.c
index be54176..6340cef 100644
--- a/arch/x86/mm/gup.c
+++ b/arch/x86/mm/gup.c
@@ -219,6 +219,22 @@ static int gup_pud_range(pgd_t pgd, unsigned long addr, unsigned long end,
 	return 1;
 }
 
+/**
+ * get_user_pages_fast() - pin user pages in memory
+ * @start:	starting user address
+ * @nr_pages:	number of pages from start to pin
+ * @write:	whether pages will be written to
+ * @pages:	array that receives pointers to the pages pinned.
+ * 		Should be at least nr_pages long.
+ *
+ * Attempt to pin user pages in memory without taking mm->mmap_sem.
+ * If not successful, it will fall back to taking the lock and
+ * calling get_user_pages().
+ *
+ * Returns number of pages pinned. This may be fewer than the number
+ * requested. If nr_pages is 0 or negative, returns 0. If no pages
+ * were pinned, returns -errno.
+ */
 int get_user_pages_fast(unsigned long start, int nr_pages, int write,
 			struct page **pages)
 {
--
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