From 9bab050913ce7f9c04e41d7f76a3eb2a0d4d4b54 Mon Sep 17 00:00:00 2001 From: Todd Kjos Date: Mon, 27 Jan 2025 20:53:47 +0000 Subject: [PATCH] ANDROID: KABI macros to release excess KABI fields for use with backports With KMI freeze, we reserve padding in structs to be exclusively used for LTS updates that would otherwise break the KMI. These fields are reserved via the ANDROID_KABI_RESERVE() macro that adds a u64 field to the struct. The ANDROID_KABI_USE() macro is used when the field is needed for an LTS patch backport. Since these fields must be reserved at KMI freeze time, we have make our best guess at what might be needed - and sometimes reserve too many fields. An example of this is the 8 ANDROID_KABI_RESERVE() fields in `struct net_device` for android13-5.15. We are now 3 years into the 6 year lifetime for android13-5.15 and none of those 8 padding fields have been used. At this point it is reasonable to allow 1 or 2 of those fields to be used for non-LTS backports. We won't relax the rule that ANDROID_KABI_RESERVE() is exclusively for LTS backports, Instead we'll introduce a new macro, ANDROID_KABI_BACKPORT_OK() to release some KABI fields for general use as the branches age and the use of padding for LTS becomes unlikely. We release the field for use by replacing the ANDROID_KABI_RESERVE() with the new ANDROID_KABI_BACKPORT_OK() macro, which has the exact same implementation, but allows others to use it for backporting features from upstream. When an ANDROID_KABI_BACKPORT_OK() field is going to be used, the ANDROID_KABI_BACKPORT_USE() macro is used to indicate that the field was used for a feature backport, not an LTS patch. This patch adds the two new macros: ANDROID_KABI_BACKPORT_OK() : exactly the same as ANDROID_KABI_RESERVE() ANDROID_KABI_BACKPORT_USE() ; exacly the same as ANDROID_KABI_USE() Patches that change an ANDROID_KABI_RESERVE() to ANDROID_KABI_BACKPORT_OK() must be reviewed and get a CR+1 from gregkh@, joneslee@ or tkjos@ to make sure it really is acceptable to reduce the padding for LTS merges. Bug: 392673958 Signed-off-by: Todd Kjos Change-Id: I19b9dfc16d891fb6fe48ec4379c6fa3dcb6adf24 (cherry picked from commit f1954b6e6cba2533beb6dff539b9d0b079ceb665) --- include/linux/android_kabi.h | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+) diff --git a/include/linux/android_kabi.h b/include/linux/android_kabi.h index 1fa329ee4d73..02ba25dbfdbf 100644 --- a/include/linux/android_kabi.h +++ b/include/linux/android_kabi.h @@ -90,6 +90,14 @@ #define ANDROID_KABI_RESERVE(number) #endif +/* + * ANDROID_KABI_BACKPORT_OK + * Used to allow padding originally reserved with ANDROID_KABI_RESERVE + * to be used for backports of non-LTS patches by partners. These + * fields can by used by replacing with ANDROID_KABI_BACKPORT_USE() + * for partner backports. + */ +#define ANDROID_KABI_BACKPORT_OK(number) ANDROID_KABI_RESERVE(number) /* * Macros to use _after_ the ABI is frozen @@ -104,6 +112,17 @@ #define ANDROID_KABI_USE(number, _new) \ _ANDROID_KABI_REPLACE(_ANDROID_KABI_RESERVE(number), _new) +/* + * ANDROID_KABI_BACKPORT_USE(number, _new) + * Use a previous padding entry that was defined with + * ANDROID_KABI_BACKPORT_OK(). This is functionally identical + * to ANDROID_KABI_USE() except that it differentiates the + * normal use of KABI fields for LTS from KABI fields that + * were released for use with other backports from upstream. + */ +#define ANDROID_KABI_BACKPORT_USE(number, _new) \ + ANDROID_KABI_USE(number, _new) + /* * ANDROID_KABI_USE2(number, _new1, _new2) * Use a previous padding entry that was defined with ANDROID_KABI_RESERVE for