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x-vs=clean score=-100 state=0 X-ME-VSCategory: clean X-CM-Envelope: MS4wfMtvQrWJvGN/pWr/j2T6+y+7+BRjk59okdYdf5KXOn8QQw0OR4ieYS843g5sHNP6vN5/AhVaGoEHeyXCkiG4YOIUYcZyzTTGLUIaxmkz7Kl7egq2c7ZO rbpzfGGqP22OC50xrZxsdobRtnVVGEKWdWQ3JYgWUfOIjRhKAXn5fy/YXS80bJ2wWGuwnKpj+pryGl3emTYPkNTL40HIde/K+aHbnGi9MUGq1q2eqa/aPuRK X-CM-Analysis: v=2.3 cv=NPP7BXyg c=1 sm=1 tr=0 a=UK1r566ZdBxH71SXbqIOeA==:117 a=UK1r566ZdBxH71SXbqIOeA==:17 a=kj9zAlcOel0A:10 a=Kd1tUaAdevIA:10 a=VwQbUJbxAAAA:8 a=Newdxa483icPIVLupAoA:9 a=CjuIK1q_8ugA:10 a=x8gzFH9gYPwA:10 a=AjGcO6oz07-iQ99wixmX:22 X-ME-CMScore: 0 X-ME-CMCategory: none Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751415AbeDFE6h (ORCPT ); Fri, 6 Apr 2018 00:58:37 -0400 Received: from zeniv.linux.org.uk ([195.92.253.2]:48582 "EHLO ZenIV.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751280AbeDFE6g (ORCPT ); Fri, 6 Apr 2018 00:58:36 -0400 Date: Fri, 6 Apr 2018 05:58:33 +0100 From: Al Viro To: Christoph Hellwig Cc: Avi Kivity , linux-aio@kvack.org, linux-fsdevel@vger.kernel.org, netdev@vger.kernel.org, linux-api@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 05/32] fs: introduce new ->get_poll_head and ->poll_mask methods Message-ID: <20180406045833.GW30522@ZenIV.linux.org.uk> References: <20180330150809.28094-1-hch@lst.de> <20180330150809.28094-6-hch@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180330150809.28094-6-hch@lst.de> User-Agent: Mutt/1.9.1 (2017-09-22) Sender: linux-api-owner@vger.kernel.org X-Mailing-List: linux-api@vger.kernel.org X-getmail-retrieved-from-mailbox: INBOX X-Mailing-List: linux-kernel@vger.kernel.org List-ID: On Fri, Mar 30, 2018 at 05:07:42PM +0200, Christoph Hellwig wrote: > + get_poll_head: Returns the struct wait_queue_head that poll, select, > + epoll or aio poll should wait on in case this instance only has single > + waitqueue. Can return NULL to indicate polling is not supported, > + or a POLL* value using the POLL_TO_PTR helper in case a grave error > + occured and ->poll_mask shall not be called. > + if (IS_ERR(head)) > + return PTR_TO_POLL(head); > + * ->get_poll_head can return a __poll_t in the PTR_ERR, use these macros > + * to return the value and recover it. It takes care of the negation as > + * well as off the annotations. > + */ > +#define POLL_TO_PTR(mask) (ERR_PTR(-(__force int)(mask))) Uh-oh... static inline bool __must_check IS_ERR(__force const void *ptr) { return IS_ERR_VALUE((unsigned long)ptr); } #define IS_ERR_VALUE(x) unlikely((unsigned long)(void *)(x) >= (unsigned long)-MAX_ERRNO) #define MAX_ERRNO 4095 IOW, your trick relies upon arguments of PTR_TO_POLL being no greater than 4095. Now, consider #define EPOLLRDHUP (__force __poll_t)0x00002000 which is to say, 8192... So anything that tries e.g. POLL_TO_PTR(EPOLLRDHUP | EPOLLERR) will be in for a quiet unpleasant surprise...