提交 672027a3 编写于 作者: I Inaky Perez-Gonzalez 提交者: Greg Kroah-Hartman

USB: add rationale on why usb descriptor structures have to be packed

Add argumentation in defense of using __attribute__((packed)) in USB
descriptors authored by Dave Brownell. Necessary as in some cases it
seems superfluous.
Signed-off-by: NInaky Perez-Gonzalez <inaky@linux.intel.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>
上级 822c7ef4
/*
* This file holds USB constants and structures that are needed for USB
* device APIs. These are used by the USB device model, which is defined
* in chapter 9 of the USB 2.0 specification. Linux has several APIs in C
* that need these:
* This file holds USB constants and structures that are needed for
* USB device APIs. These are used by the USB device model, which is
* defined in chapter 9 of the USB 2.0 specification and in the
* Wireless USB 1.0 (spread around). Linux has several APIs in C that
* need these:
*
* - the master/host side Linux-USB kernel driver API;
* - the "usbfs" user space API; and
......@@ -14,6 +15,19 @@
*
* There's also "Wireless USB", using low power short range radios for
* peripheral interconnection but otherwise building on the USB framework.
*
* Note all descriptors are declared '__attribute__((packed))' so that:
*
* [a] they never get padded, either internally (USB spec writers
* probably handled that) or externally;
*
* [b] so that accessing bigger-than-a-bytes fields will never
* generate bus errors on any platform, even when the location of
* its descriptor inside a bundle isn't "naturally aligned", and
*
* [c] for consistency, removing all doubt even when it appears to
* someone that the two other points are non-issues for that
* particular descriptor type.
*/
#ifndef __LINUX_USB_CH9_H
......
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