From a0d22f485af1553060b4094ee0154537a8f6a8a6 Mon Sep 17 00:00:00 2001 From: Andy Grover Date: Thu, 9 Apr 2009 16:45:29 -0700 Subject: [PATCH] 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 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 --- arch/x86/mm/gup.c | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) diff --git a/arch/x86/mm/gup.c b/arch/x86/mm/gup.c index be54176e9eb2..6340cef6798a 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) { -- 2.20.1