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Date: Wed, 11 Apr 2012 14:02:00 -0300
From: Mauro Carvalho Chehab <mchehab@...hat.com>
To: Rémi Denis-Courmont <remi@...lab.net>
CC: mchehab@...radead.org, linux-media@...r.kernel.org,
linux-kernel@...r.kernel.org, Alan Cox <alan@...rguk.ukuu.org.uk>
Subject: Re: [RFC] [PATCH] v4l2: use unsigned rather than enums in ioctl()
structs
Em 05-04-2012 14:52, Rémi Denis-Courmont escreveu:
> With an enumeration, the compiler assumes that the integer value is one
> allowed by the underlying enumeration type. With optimization enabled
> this can result in byte code that is unable to cope with other values.
> For instance, GCC can compile a switch() block using a "jump table" to
> avoid repetitive conditional branching.
>
> This can be a problem both from user to kernel and kernel to user.
>
> * Evil user space can pass error values to the kernel via system
> calls. There are no sane ways to protect the kernel: the compiler may
> optimize away range checks if it deems that all legitimate values are
> within the range.
>
> * The kernel can break the user space binary interface whenever a new
> value is added to an existing enumeration. A newer kernel can then
> return an enumerated value that was not allowed by older kernel headers
> against which the user program was compiled. In principles, V4L2 user
> space needs to be recompiled whenever videodev2.h has updated enums...
> (This an obvious problem with V4L2_QUERYCTRL.)
>
> Fortunately, the Linux ABI disables short-enums on all platforms. Even
> the Linux variant of the ARM AAPCS contradicts the standard ARM AAPCS
> in doing so.
Using unsigned instead of enum is not a good idea, from API POV, as unsigned
has different sizes on 32 bits and 64 bits. Yet, using enum was really a very
bad idea, and, on all new stuff, we're not accepting any new enum field.
That's said, a patch like that were proposed in the past. See:
http://www.spinics.net/lists/vfl/msg25686.html
Alan said there [1] that:
"Its a fundamental change to a public structure from enum to u32. I think you
are right but this change seems too late by several years."
I also didn't like it, because of the same reasons.
[1] http://www.spinics.net/lists/vfl/msg25687.html
I don't think anything has changed since then that would make it easier
to apply a change like that.
Well, eventually, a compat code at the v4l2-ioctl.c might be written to translate
a call if the enum size is different than the integer size.
Regards,
Mauro
>
> Signed-off-by: Rémi Denis-Courmont <remi@...lab.net>
> ---
> include/linux/videodev2.h | 42 +++++++++++++++++++++---------------------
> 1 file changed, 21 insertions(+), 21 deletions(-)
>
> diff --git a/include/linux/videodev2.h b/include/linux/videodev2.h
> index c9c9a46..df3b8f0 100644
> --- a/include/linux/videodev2.h
> +++ b/include/linux/videodev2.h
> @@ -292,10 +292,10 @@ struct v4l2_pix_format {
> __u32 width;
> __u32 height;
> __u32 pixelformat;
> - enum v4l2_field field;
> + unsigned field;
> __u32 bytesperline; /* for padding, zero if unused */
> __u32 sizeimage;
> - enum v4l2_colorspace colorspace;
> + unsigned colorspace;
> __u32 priv; /* private data, depends on pixelformat */
> };
>
> @@ -432,7 +432,7 @@ struct v4l2_pix_format {
> */
> struct v4l2_fmtdesc {
> __u32 index; /* Format number */
> - enum v4l2_buf_type type; /* buffer type */
> + unsigned type; /* buffer type */
> __u32 flags;
> __u8 description[32]; /* Description string */
> __u32 pixelformat; /* Format fourcc */
> @@ -573,8 +573,8 @@ struct v4l2_jpegcompression {
> */
> struct v4l2_requestbuffers {
> __u32 count;
> - enum v4l2_buf_type type;
> - enum v4l2_memory memory;
> + unsigned type;
> + unsigned memory;
> __u32 reserved[2];
> };
>
> @@ -636,16 +636,16 @@ struct v4l2_plane {
> */
> struct v4l2_buffer {
> __u32 index;
> - enum v4l2_buf_type type;
> + unsigned type;
> __u32 bytesused;
> __u32 flags;
> - enum v4l2_field field;
> + unsigned field;
> struct timeval timestamp;
> struct v4l2_timecode timecode;
> __u32 sequence;
>
> /* memory location */
> - enum v4l2_memory memory;
> + unsigned memory;
> union {
> __u32 offset;
> unsigned long userptr;
> @@ -708,7 +708,7 @@ struct v4l2_clip {
>
> struct v4l2_window {
> struct v4l2_rect w;
> - enum v4l2_field field;
> + unsigned field;
> __u32 chromakey;
> struct v4l2_clip __user *clips;
> __u32 clipcount;
> @@ -745,14 +745,14 @@ struct v4l2_outputparm {
> * I N P U T I M A G E C R O P P I N G
> */
> struct v4l2_cropcap {
> - enum v4l2_buf_type type;
> + unsigned type;
> struct v4l2_rect bounds;
> struct v4l2_rect defrect;
> struct v4l2_fract pixelaspect;
> };
>
> struct v4l2_crop {
> - enum v4l2_buf_type type;
> + unsigned type;
> struct v4l2_rect c;
> };
>
> @@ -1156,7 +1156,7 @@ enum v4l2_ctrl_type {
> /* Used in the VIDIOC_QUERYCTRL ioctl for querying controls */
> struct v4l2_queryctrl {
> __u32 id;
> - enum v4l2_ctrl_type type;
> + unsigned type;
> __u8 name[32]; /* Whatever */
> __s32 minimum; /* Note signedness */
> __s32 maximum;
> @@ -1788,7 +1788,7 @@ enum v4l2_jpeg_chroma_subsampling {
> struct v4l2_tuner {
> __u32 index;
> __u8 name[32];
> - enum v4l2_tuner_type type;
> + unsigned type;
> __u32 capability;
> __u32 rangelow;
> __u32 rangehigh;
> @@ -1838,14 +1838,14 @@ struct v4l2_modulator {
>
> struct v4l2_frequency {
> __u32 tuner;
> - enum v4l2_tuner_type type;
> + unsigned type;
> __u32 frequency;
> __u32 reserved[8];
> };
>
> struct v4l2_hw_freq_seek {
> __u32 tuner;
> - enum v4l2_tuner_type type;
> + unsigned type;
> __u32 seek_upward;
> __u32 wrap_around;
> __u32 spacing;
> @@ -2056,7 +2056,7 @@ struct v4l2_sliced_vbi_cap {
> (equals frame lines 313-336 for 625 line video
> standards, 263-286 for 525 line standards) */
> __u16 service_lines[2][24];
> - enum v4l2_buf_type type;
> + unsigned type;
> __u32 reserved[3]; /* must be 0 */
> };
>
> @@ -2146,8 +2146,8 @@ struct v4l2_pix_format_mplane {
> __u32 width;
> __u32 height;
> __u32 pixelformat;
> - enum v4l2_field field;
> - enum v4l2_colorspace colorspace;
> + unsigned field;
> + unsigned colorspace;
>
> struct v4l2_plane_pix_format plane_fmt[VIDEO_MAX_PLANES];
> __u8 num_planes;
> @@ -2165,7 +2165,7 @@ struct v4l2_pix_format_mplane {
> * @raw_data: placeholder for future extensions and custom formats
> */
> struct v4l2_format {
> - enum v4l2_buf_type type;
> + unsigned type;
> union {
> struct v4l2_pix_format pix; /* V4L2_BUF_TYPE_VIDEO_CAPTURE */
> struct v4l2_pix_format_mplane pix_mp; /* V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE */
> @@ -2179,7 +2179,7 @@ struct v4l2_format {
> /* Stream type-dependent parameters
> */
> struct v4l2_streamparm {
> - enum v4l2_buf_type type;
> + unsigned type;
> union {
> struct v4l2_captureparm capture;
> struct v4l2_outputparm output;
> @@ -2299,7 +2299,7 @@ struct v4l2_dbg_chip_ident {
> struct v4l2_create_buffers {
> __u32 index;
> __u32 count;
> - enum v4l2_memory memory;
> + unsigned memory;
> struct v4l2_format format;
> __u32 reserved[8];
> };
--
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