Commit 1d338b86 authored by Mauro Carvalho Chehab's avatar Mauro Carvalho Chehab

media: v4l2-compat-ioctl32: better document the code

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().
Reviewed-by: default avatarHans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: default avatarMauro Carvalho Chehab <mchehab@s-opensource.com>
parent 09c033b6
......@@ -22,7 +22,18 @@
#include <media/v4l2-ctrls.h>
#include <media/v4l2-ioctl.h>
/* 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 a 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;
......@@ -1010,6 +1085,13 @@ 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)
......@@ -1038,6 +1120,21 @@ 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)
{
......@@ -1049,6 +1146,23 @@ 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);
......@@ -1058,7 +1172,9 @@ 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;
......@@ -1087,6 +1203,11 @@ 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:
......@@ -1209,6 +1330,15 @@ 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
......@@ -1218,9 +1348,14 @@ 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:
......@@ -1237,6 +1372,10 @@ 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:
......@@ -1287,6 +1426,20 @@ 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);
......
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