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 <mchehab@xxxxxxxxxxxxxxxx>
---
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 <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 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);
--
2.14.3
