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Re: Linux kernel version support policy


On Mon, 27 Jan 2014, Mike Frysinger wrote:

> i'm not saying the changes to actually remove support has to be written first.  
> i'm saying we should have an idea of what conditionals would get cleaned up 
> and how many files/LoC are actually impacted.

Well, supposing 2.6.32 were the version used, in the generic Linux 
kernel-features.h this appears to affect __ASSUME_UTIMES, 
__ASSUME_PSELECT, __ASSUME_PPOLL, __ASSUME_ATFCTS, 
__ASSUME_SET_ROBUST_LIST, __ASSUME_COMPLETE_READV_WRITEV, 
__ASSUME_FUTEX_LOCK_PI, __ASSUME_UTIMENSAT, __ASSUME_PRIVATE_FUTEX, 
__ASSUME_FALLOCATE, __ASSUME_O_CLOEXEC, __ASSUME_ARG_MAX_STACK_BASED, 
__ASSUME_ADJ_OFFSET_SS_READ, __ASSUME_SOCK_CLOEXEC, __ASSUME_IN_NONBLOCK, 
__ASSUME_PIPE2, __ASSUME_EVENTFD2, __ASSUME_SIGNALFD4, __ASSUME_DUP3, 
__ASSUME_ACCEPT4, __ASSUME_FUTEX_CLOCK_REALTIME, __ASSUME_AT_RANDOM, 
__ASSUME_PREADV, __ASSUME_PWRITEV, __ASSUME_REQUEUE_PI, 
__ASSUME_F_GETOWN_EX and __ASSUME_XFS_RESTRICTED_CHOWN.  I haven't checked 
what code is conditioned by these (and in some cases it's not 
Linux-specific code, in which case conditionals can't be removed 
completely unless Hurd also supports the feature, or the macros would 
still only be defined for some architectures), but for example there's a 
bug report about the pselect fallback which could be closed if that 
fallback could go away (unfortunately, it appears it wasn't added until 
3.0 for m68k), and loads of code conditional on __ASSUME_ATFCTS (where the 
fallbacks allocate an arbitrary-size buffer with alloca, meaning stack 
overflow for huge filenames, and use snprintf with non-obvious 
consequences for signal-safety - could those uses of snprintf use 
malloc?).

-- 
Joseph S. Myers
joseph@codesourcery.com


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