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8b7fd6a15f
Currently, hid_bpf_rdesc_fixup() is called once the match between the
HID device and the driver is done. This can be problematic in case
the driver selected by the kernel would change the report descriptor
after the fact.
To give a chance for hid_bpf_rdesc_fixup() to provide hints on to how
to select a dedicated driver or not, move the call to that BPF hook
earlier in the .probe() process, when we get the first match.
However, this means that we might get called more than once (typically
once for hid-generic, and once for hid-vendor-specific). So we store the
result of HID-BPF fixup in struct hid_device. Basically, this means that
->bpf_rdesc can replace ->dev_rdesc when it was used in the code.
In order to not grow struct hid_device, some fields are re-ordered. This
was the output of pahole for the first 128 bytes:
struct hid_device {
__u8 * dev_rdesc; /* 0 8 */
unsigned int dev_rsize; /* 8 4 */
/* XXX 4 bytes hole, try to pack */
__u8 * rdesc; /* 16 8 */
unsigned int rsize; /* 24 4 */
/* XXX 4 bytes hole, try to pack */
struct hid_collection * collection; /* 32 8 */
unsigned int collection_size; /* 40 4 */
unsigned int maxcollection; /* 44 4 */
unsigned int maxapplication; /* 48 4 */
__u16 bus; /* 52 2 */
__u16 group; /* 54 2 */
__u32 vendor; /* 56 4 */
__u32 product; /* 60 4 */
/* --- cacheline 1 boundary (64 bytes) --- */
__u32 version; /* 64 4 */
enum hid_type type; /* 68 4 */
unsigned int country; /* 72 4 */
/* XXX 4 bytes hole, try to pack */
struct hid_report_enum report_enum[3]; /* 80 6216 */
Basically, we got three holes of 4 bytes. We can reorder things a little
and makes those 3 holes a continuous 12 bytes hole, which can be replaced
by the new pointer and the new unsigned int we need.
In terms of code allocation, when not using HID-BPF, we are back to kernel
v6.2 in hid_open_report(). These multiple kmemdup() calls will be fixed
in a later commit.
Link: https://patch.msgid.link/20241001-hid-bpf-hid-generic-v3-1-2ef1019468df@kernel.org
Signed-off-by: Benjamin Tissoires <bentiss@kernel.org>
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.