From patchwork Fri Apr 20 11:45:46 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Mauro Carvalho Chehab X-Patchwork-Id: 10352489 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id E412D60365 for ; Fri, 20 Apr 2018 11:45:54 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id D353228574 for ; Fri, 20 Apr 2018 11:45:54 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id C6B4E286E4; Fri, 20 Apr 2018 11:45:54 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.9 required=2.0 tests=BAYES_00, MAILING_LIST_MULTI, RCVD_IN_DNSWL_HI autolearn=ham version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id D300C28574 for ; Fri, 20 Apr 2018 11:45:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754619AbeDTLpw (ORCPT ); Fri, 20 Apr 2018 07:45:52 -0400 Received: from osg.samsung.com ([64.30.133.232]:62992 "EHLO osg.samsung.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754591AbeDTLpw (ORCPT ); Fri, 20 Apr 2018 07:45:52 -0400 Received: from localhost (localhost [127.0.0.1]) by osg.samsung.com (Postfix) with ESMTP id E033F37B48; Fri, 20 Apr 2018 04:45:51 -0700 (PDT) X-Virus-Scanned: Debian amavisd-new at dev.s-opensource.com Received: from osg.samsung.com ([127.0.0.1]) by localhost (localhost [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id uzZ98wED9HzW; Fri, 20 Apr 2018 04:45:50 -0700 (PDT) Received: from smtp.s-opensource.com (unknown [179.179.47.30]) by osg.samsung.com (Postfix) with ESMTPSA id 6EA8937B3F; Fri, 20 Apr 2018 04:45:50 -0700 (PDT) Received: from mchehab by smtp.s-opensource.com with local (Exim 4.90_1) (envelope-from ) id 1f9UU8-0007yt-9x; Fri, 20 Apr 2018 07:45:48 -0400 From: Mauro Carvalho Chehab Cc: Mauro Carvalho Chehab , Linux Media Mailing List , Mauro Carvalho Chehab , Hans Verkuil , Sakari Ailus , Daniel Mentz Subject: [PATCH v2] media: v4l2-compat-ioctl32: better document the code Date: Fri, 20 Apr 2018 07:45:46 -0400 Message-Id: <3669995510390091ef07287ff313974c15b141b2.1524224727.git.mchehab@s-opensource.com> X-Mailer: git-send-email 2.14.3 In-Reply-To: References: To: unlisted-recipients:; (no To-header on input) Sender: linux-media-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-media@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP This file does a lot of non-trivial struff. Document it using kernel-doc markups where needed and improve the comments inside do_video_ioctl(). Signed-off-by: Mauro Carvalho Chehab Reviewed-by: Hans Verkuil --- drivers/media/v4l2-core/v4l2-compat-ioctl32.c | 165 +++++++++++++++++++++++++- 1 file changed, 159 insertions(+), 6 deletions(-) diff --git a/drivers/media/v4l2-core/v4l2-compat-ioctl32.c b/drivers/media/v4l2-core/v4l2-compat-ioctl32.c index d2f0268427c2..9611c3aae8ca 100644 --- a/drivers/media/v4l2-core/v4l2-compat-ioctl32.c +++ b/drivers/media/v4l2-core/v4l2-compat-ioctl32.c @@ -22,7 +22,18 @@ #include #include -/* Use the same argument order as copy_in_user */ +/** + * assign_in_user() - Copy from one __user var to another one + * + * @to: __user var where data will be stored + * @from: __user var where data will be retrieved. + * + * As this code very often needs to allocate userspace memory, it is easier + * to have a macro that will do both get_user() and put_user() at once. + * + * This function complements the macros defined at asm-generic/uaccess.h. + * It uses the same argument order as copy_in_user() + */ #define assign_in_user(to, from) \ ({ \ typeof(*from) __assign_tmp; \ @@ -30,16 +41,56 @@ get_user(__assign_tmp, from) || put_user(__assign_tmp, to); \ }) +/** + * get_user_cast() - Stores at a kernelspace local var the contents from a + * pointer with userspace data that is not tagged with __user. + * + * @__x: var where data will be stored + * @__ptr: var where data will be retrieved. + * + * Sometimes we need to declare a pointer without __user because it + * comes from a pointer struct field that will be retrieved from userspace + * by the 64-bit native ioctl handler. This function ensures that the + * @__ptr will be cast to __user before calling get_user() in order to + * avoid warnings with static code analyzers like smatch. + */ #define get_user_cast(__x, __ptr) \ ({ \ get_user(__x, (typeof(*__ptr) __user *)(__ptr)); \ }) +/** + * put_user_force() - Stores the contents of a kernelspace local var + * into an userspace pointer, removing any __user cast. + * + * @__x: var where data will be stored + * @__ptr: var where data will be retrieved. + * + * Sometimes we need to remove the __user attribute from some data, + * by passing the __force macro. This function ensures that the + * @__ptr will be cast with __force before calling put_user(), in order to + * avoid warnings with static code analyzers like smatch. + */ #define put_user_force(__x, __ptr) \ ({ \ put_user((typeof(*__x) __force *)(__x), __ptr); \ }) +/** + * assign_in_user_cast() - Copy from one __user var to another one + * + * @to: __user var where data will be stored + * @from: var where data will be retrieved that needs to be cast to __user. + * + * As this code very often needs to allocate userspace memory, it is easier + * to have a macro that will do both get_user_cast() and put_user() at once. + * + * This function should be used instead of assign_in_user() when the @from + * variable was not declared as __user. See get_user_cast() for more details. + * + * This function complements the macros defined at asm-generic/uaccess.h. + * It uses the same argument order as copy_in_user() + */ #define assign_in_user_cast(to, from) \ ({ \ typeof(*from) __assign_tmp; \ @@ -47,7 +98,16 @@ get_user_cast(__assign_tmp, from) || put_user(__assign_tmp, to);\ }) - +/** + * native_ioctl - Ancillary function that calls the native 64 bits ioctl + * handler. + * + * @file: pointer to &struct file with the file handler + * @cmd: ioctl to be called + * @arg: arguments passed from/to the ioctl handler + * + * This function calls the native ioctl handler at v4l2-dev, e. g. v4l2_ioctl() + */ static long native_ioctl(struct file *file, unsigned int cmd, unsigned long arg) { long ret = -ENOIOCTLCMD; @@ -59,6 +119,21 @@ static long native_ioctl(struct file *file, unsigned int cmd, unsigned long arg) } +/* + * Per-ioctl data copy handlers. + * + * Those come in pairs, with a get_v4l2_foo() and a put_v4l2_foo() routine, + * where "v4l2_foo" is the name of the V4L2 struct. + * + * They basically get two __user pointers, one with a 32-bits struct that + * came from the userspace call and a 64-bits struct, also allocated as + * userspace, but filled internally by do_video_ioctl(). + * + * For ioctls that have pointers inside it, the functions will also + * receive an ancillary buffer with extra space, used to pass extra + * data to the routine. + */ + struct v4l2_clip32 { struct v4l2_rect c; compat_caddr_t next; @@ -1009,6 +1084,13 @@ static int put_v4l2_edid32(struct v4l2_edid __user *p64, return 0; } +/* + * List of ioctls that require 32-bits/64-bits conversion + * + * The V4L2 ioctls that aren't listed there don't have pointer arguments + * and the struct size is identical for both 32 and 64 bits versions, so + * they don't need translations. + */ #define VIDIOC_G_FMT32 _IOWR('V', 4, struct v4l2_format32) #define VIDIOC_S_FMT32 _IOWR('V', 5, struct v4l2_format32) @@ -1037,6 +1119,21 @@ static int put_v4l2_edid32(struct v4l2_edid __user *p64, #define VIDIOC_G_OUTPUT32 _IOR ('V', 46, s32) #define VIDIOC_S_OUTPUT32 _IOWR('V', 47, s32) +/** + * alloc_userspace() - Allocates a 64-bits userspace pointer compatible + * for calling the native 64-bits version of an ioctl. + * + * @size: size of the structure itself to be allocated. + * @aux_space: extra size needed to store "extra" data, e.g. space for + * other __user data that is pointed to fields inside the + * structure. + * @new_p64: pointer to a pointer to be filled with the allocated struct. + * + * Return: + * + * if it can't allocate memory, either -ENOMEM or -EFAULT will be returned. + * Zero otherwise. + */ static int alloc_userspace(unsigned int size, u32 aux_space, void __user **new_p64) { @@ -1048,6 +1145,23 @@ static int alloc_userspace(unsigned int size, u32 aux_space, return 0; } +/** + * do_video_ioctl() - Ancillary function with handles a compat32 ioctl call + * + * @file: pointer to &struct file with the file handler + * @cmd: ioctl to be called + * @arg: arguments passed from/to the ioctl handler + * + * This function is called when a 32 bits application calls a V4L2 ioctl + * and the Kernel is compiled with 64 bits. + * + * This function is called by v4l2_compat_ioctl32() when the function is + * not private to some specific driver. + * + * It converts a 32-bits struct into a 64 bits one, calls the native 64-bits + * ioctl handler and fills back the 32-bits struct with the results of the + * native call. + */ static long do_video_ioctl(struct file *file, unsigned int cmd, unsigned long arg) { void __user *p32 = compat_ptr(arg); @@ -1057,7 +1171,9 @@ static long do_video_ioctl(struct file *file, unsigned int cmd, unsigned long ar int compatible_arg = 1; long err = 0; - /* First, convert the command. */ + /* + * 1. When struct size is different, converts the command. + */ switch (cmd) { case VIDIOC_G_FMT32: cmd = VIDIOC_G_FMT; break; case VIDIOC_S_FMT32: cmd = VIDIOC_S_FMT; break; @@ -1086,6 +1202,11 @@ static long do_video_ioctl(struct file *file, unsigned int cmd, unsigned long ar case VIDIOC_S_EDID32: cmd = VIDIOC_S_EDID; break; } + /* + * 2. Allocates a 64-bits userspace pointer to store the + * values of the ioctl and copy data from the 32-bits __user + * argument into it. + */ switch (cmd) { case VIDIOC_OVERLAY: case VIDIOC_STREAMON: @@ -1208,6 +1329,15 @@ static long do_video_ioctl(struct file *file, unsigned int cmd, unsigned long ar if (err) return err; + /* + * 3. Calls the native 64-bits ioctl handler. + * + * For the functions where a conversion was not needed, + * compatible_arg is true, and it will call it with the arguments + * provided by userspace and stored at @p32 var. + * + * Otherwise, it will pass the newly allocated @new_p64 argument. + */ if (compatible_arg) err = native_ioctl(file, cmd, (unsigned long)p32); else @@ -1217,9 +1347,14 @@ static long do_video_ioctl(struct file *file, unsigned int cmd, unsigned long ar return err; /* - * Special case: even after an error we need to put the - * results back for these ioctls since the error_idx will - * contain information on which control failed. + * 4. Special case: even after an error we need to put the + * results back for some ioctls. + * + * In the case of EXT_CTRLS, the error_idx will contain information + * on which control failed. + * + * In the case of S_EDID, the driver can return E2BIG and set + * the blocks to maximum allowed value. */ switch (cmd) { case VIDIOC_G_EXT_CTRLS: @@ -1236,6 +1371,10 @@ static long do_video_ioctl(struct file *file, unsigned int cmd, unsigned long ar if (err) return err; + /* + * 5. Copy the data returned at the 64 bits userspace pointer to + * the original 32 bits structure. + */ switch (cmd) { case VIDIOC_S_INPUT: case VIDIOC_S_OUTPUT: @@ -1286,6 +1425,20 @@ static long do_video_ioctl(struct file *file, unsigned int cmd, unsigned long ar return err; } +/** + * v4l2_compat_ioctl32() - Handles a compat32 ioctl call + * + * @file: pointer to &struct file with the file handler + * @cmd: ioctl to be called + * @arg: arguments passed from/to the ioctl handler + * + * This function is meant to be used as .compat_ioctl fops at v4l2-dev.c + * in order to deal with 32-bit calls on a 64-bits Kernel. + * + * This function calls do_video_ioctl() for non-private V4L2 ioctls. + * If the function is a private one it calls vdev->fops->compat_ioctl32 + * instead. + */ long v4l2_compat_ioctl32(struct file *file, unsigned int cmd, unsigned long arg) { struct video_device *vdev = video_devdata(file);