From mboxrd@z Thu Jan 1 00:00:00 1970 From: Vitaly Mayatskikh Subject: [PATCH 1/2] Introduce check_readable_bytes() Date: Thu, 14 May 2009 18:19:00 +0200 Message-ID: <1242317939-15392-2-git-send-email-v.mayatskih@gmail.com> References: <1242317939-15392-1-git-send-email-v.mayatskih@gmail.com> Cc: sandeen@redhat.com, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org To: Josef Bacik Return-path: Received: from mail-fx0-f158.google.com ([209.85.220.158]:34138 "EHLO mail-fx0-f158.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752881AbZENQTJ (ORCPT ); Thu, 14 May 2009 12:19:09 -0400 In-Reply-To: <1242317939-15392-1-git-send-email-v.mayatskih@gmail.com> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: This routine acts almost as fault_in_pages_readable(), but returns accessible amount of bytes instead of plain OK/FAIL, so callers may know how many data can be proceeded without GPF. Signed-off-by: Vitaly Mayatskikh --- include/linux/pagemap.h | 35 +++++++++++++++++++++++++++++++++++ 1 files changed, 35 insertions(+), 0 deletions(-) diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h index 34da523..f931308 100644 --- a/include/linux/pagemap.h +++ b/include/linux/pagemap.h @@ -439,6 +439,41 @@ static inline int fault_in_pages_readable(const char __user *uaddr, int size) return ret; } +/* + * check_readable_bytes - check if given amount of bytes can be read + * at given address. + * @uaddr: address to check + * @size: size to check + * + * Returns 0 when @size is 0, -EFAULT when @uaddr points to + * unaccessible region, or count of accessible bytes. + */ +static inline int check_readable_bytes(const char __user *uaddr, int size) +{ + volatile char c; + int ret = 0; + long page_begin = (unsigned long)uaddr & PAGE_MASK; + long page_end = ((unsigned long)uaddr + size) & PAGE_MASK; + long ptr = page_begin; + + if (unlikely(size == 0)) + goto out; + + while (!ret && ptr <= page_end) { + ret = __get_user(c, (const char __user*)ptr); + if (!ret) + ptr += PAGE_SIZE; + } + + if (likely(!ret)) + ret = size; + else + ret = (ptr == page_begin) ? + -EFAULT : (const char __user *)ptr - uaddr; +out: + return ret; +} + int add_to_page_cache_locked(struct page *page, struct address_space *mapping, pgoff_t index, gfp_t gfp_mask); int add_to_page_cache_lru(struct page *page, struct address_space *mapping, -- 1.6.2.2