From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751666AbeEVQan (ORCPT ); Tue, 22 May 2018 12:30:43 -0400 Received: from mail-io0-f194.google.com ([209.85.223.194]:45404 "EHLO mail-io0-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751557AbeEVQaj (ORCPT ); Tue, 22 May 2018 12:30:39 -0400 X-Google-Smtp-Source: AB8JxZrpsSuz/jTZXzFPF6YmSzfOVRY/f6sRXvEYo5wTKzAc98cCpo5kfhWv7B0GNN/0hY/9LUVhNA== Subject: Re: [PATCH v6 2/5] fs: Convert kiocb rw_hint from enum to u16 To: Goldwyn Rodrigues , adam.manzanares@wdc.com, viro@zeniv.linux.org.uk, linux-fsdevel@vger.kernel.org, bcrl@kvack.org Cc: tglx@linutronix.de, mingo@kernel.org, pombredanne@nexb.com, kstewart@linuxfoundation.org, gregkh@linuxfoundation.org, bigeasy@linutronix.de, jack@suse.cz, darrick.wong@oracle.com, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, linux-aio@kvack.org, linux-api@vger.kernel.org, hch@infradread.org, jmoyer@redhat.com References: <20180522150737.9893-1-adam.manzanares@wdc.com> <20180522150737.9893-3-adam.manzanares@wdc.com> <11fb2ee5-8352-2d35-3154-68637d99b096@kernel.dk> <084d253c-52ab-7b23-521c-28602c56153b@suse.de> From: Jens Axboe Message-ID: <58087b03-a3c7-93fd-d1ad-de77181e8806@kernel.dk> Date: Tue, 22 May 2018 10:30:36 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.0 MIME-Version: 1.0 In-Reply-To: <084d253c-52ab-7b23-521c-28602c56153b@suse.de> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 5/22/18 10:24 AM, Goldwyn Rodrigues wrote: > > > On 05/22/2018 10:32 AM, Jens Axboe wrote: >> On 5/22/18 9:07 AM, adam.manzanares@wdc.com wrote: >>> From: Adam Manzanares >>> >>> In order to avoid kiocb bloat for per command iopriority support, rw_hint >>> is converted from enum to a u16. Added a guard around ki_hint assignment. >>> >>> Signed-off-by: Adam Manzanares >>> Reviewed-by: Christoph Hellwig >>> --- >>> include/linux/fs.h | 13 +++++++++++-- >>> 1 file changed, 11 insertions(+), 2 deletions(-) >>> >>> diff --git a/include/linux/fs.h b/include/linux/fs.h >>> index 7f07977bdfd7..50de40dbbb85 100644 >>> --- a/include/linux/fs.h >>> +++ b/include/linux/fs.h >>> @@ -284,6 +284,8 @@ enum rw_hint { >>> WRITE_LIFE_EXTREME = RWH_WRITE_LIFE_EXTREME, >>> }; >>> >>> +#define MAX_KI_HINT ((1 << 16) - 1) /* ki_hint type is u16 */ >> >> Instead of having to do this and now rely on those now being synced, >> how about something like the below. >> >> diff --git a/include/linux/fs.h b/include/linux/fs.h >> index 760d8da1b6c7..070438d0b62d 100644 >> --- a/include/linux/fs.h >> +++ b/include/linux/fs.h >> @@ -299,7 +299,7 @@ struct kiocb { >> void (*ki_complete)(struct kiocb *iocb, long ret, long ret2); >> void *private; >> int ki_flags; >> - enum rw_hint ki_hint; >> + u16 ki_hint; >> } __randomize_layout; >> >> static inline bool is_sync_kiocb(struct kiocb *kiocb) >> @@ -1927,12 +1927,22 @@ static inline enum rw_hint file_write_hint(struct file *file) >> >> static inline int iocb_flags(struct file *file); >> >> +static inline u16 ki_hint_validate(enum rw_hint hint) >> +{ >> + typeof(((struct kiocb *)0)->ki_hint) max_hint = -1; > > This looks complex to me. Would force a reader to lookback at what > datatype ki_hint is. I'd prefer to declare it as u16 max_hint = -1, or > even the previous #define MAX_KI_HINT format is easier to read. Just a > program reading style you are comfortable with though. How is it complex? It's defining a type that'll be the same as ki_hint in the kiocb, which is _exactly_ what we care about. Any sort of other definition will rely on those two locations now being synced. The above will never break. So I strongly disagree. The above will _never_ require the reader to figure out what the type is. Any other variant will _always_ require the reader to check if they are the same. -- Jens Axboe