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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@oracle.com>
AuthorDate: Thu, 9 Apr 2009 16:45:29 -0700
Committer: Ingo Molnar <mingo@elte.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@oracle.com>
Cc: npiggin@suse.de
Cc: akpm@linux-foundation.org
LKML-Reference: <1239320729-3262-1-git-send-email-andy.grover@oracle.com>
Signed-off-by: Ingo Molnar <mingo@elte.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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