On s390x, POSIX_FADV_DONTNEED and POSIX_FADV_NOREUSE have different
values than on all other architectures that Linux supports.
Handle this difference by wrapping their definitions in
include/fcntl.h in #ifdef, so that arch/s390x/bits/fcntl.h can
override them.
for getting/setting write lifetime hints fcntl commands were
added in linux commit c75b1d9421f80f4143e389d2d50ddfc8a28c8c35
added under _GNU_SOURCE || _BSD_SOURCE, since RWH_* life time
hints are not in the POSIX reserved namespace.
placing the opening brace on the same line as the struct keyword/tag
is the style I prefer and seems to be the prevailing practice in more
recent additions.
these changes were generated by the command:
find include/ arch/*/bits -name '*.h' \
-exec sed -i '/^struct [^;{]*$/{N;s/\n/ /;}' {} +
and subsequently checked by hand to ensure that the regex did not pick
up any false positives.
while it's the same for all presently supported archs, it differs at
least on sparc, and conceptually it's no less arch-specific than the
other O_* macros. O_SEARCH and O_EXEC are still defined in terms of
O_PATH in the main fcntl.h.
new in linux v3.17 commit 40e041a2c858b3caefc757e26cb85bfceae5062b
sealing allows some operations to be blocked on a file which makes
file access safer when fds are shared between processes (only
supported for shared mem fds currently)
flags:
F_SEAL_SEAL prevents further sealing
F_SEAL_SHRINK prevents file from shrinking
F_SEAL_GROW prevents file from growing
F_SEAL_WRITE prevents writes
fcntl commands:
F_GET_SEALS get the current seal flags
F_ADD_SEALS add new seal flags
open file description locks are inherited across fork and only auto
dropped after the last fd of the file description is closed, they can be
used to synchronize between threads that open separate file descriptions
for the same file.
new in linux 3.15 commit 0d3f7a2dd2f5cf9642982515e020c1aee2cf7af6
fcntl.h: AT_* is not a reserved namespace so extensions cannot be
exposed by default.
langinfo.h: YESSTR and NOSTR were removed from the standard.
limits.h: NL_NMAX was removed from the standard.
signal.h: the conditional for NSIG was wrongly checking _XOPEN_SOURCE
rather than _BSD_SOURCE. this was purely a mistake; it doesn't even
match the commit message from the commit that added it.
put some macros that do not differ between architectures in the
main header and remove from bits.
restructure mips header so it has the same structure as the others.
I'm not 100% sure that Linux's O_PATH meets the POSIX requirements for
O_SEARCH, but it seems very close if not perfect. and old kernels
ignore it, so O_SEARCH will still work as desired as long as the
caller has read permissions to the directory.
this is equivalent to posix_fallocate except that it has an extra
mode/flags argument to control its behavior, and stores the error in
errno rather than returning an error code.
the old behavior of exposing nothing except plain ISO C can be
obtained by defining __STRICT_ANSI__ or using a compiler option (such
as -std=c99) that predefines it. the new default featureset is POSIX
with XSI plus _BSD_SOURCE. any explicit feature test macros will
inhibit the default.
installation docs have also been updated to reflect this change.
so far, this is the only actual use of loff_t i've found. some
software, including glib, assumes loff_t must exist if splice exists;
this is a reasonable assumption since the official prototype for
splice uses loff_t, as it always works with 64-bit offsets regardless
of the selected libc off_t size. i'm using #define for now rather than
a typedef to make it easy to define in other headers if necessary
(like the LFS64 ugliness), but it may be necessary to add it to
alltypes.h eventually if other functions end up needing it.
on old kernels, there's no way to detect errors; we must assume
negative syscall return values are pgrp ids. but if the F_GETOWN_EX
fcntl works, we can get a reliable answer.
this is ugly and stupid, but now that the *64 symbol names exist, a
lot of broken GNU software detects them in configure, then either
breaks during build due to missing off64_t definition, or attempts to
compile without function declarations/prototypes. "fixing" it here is
easier than telling everyone to add yet another feature test macro to
their builds.
there is no reason to avoid multiple identical macro definitions; this
is perfectly legal C, and even with the maximal warning options
enabled, gcc does not issue any warning for it.
musl does not support legacy 32-bit-off_t whatsoever. off_t is always
64 bit, and correct programs that use off_t and the standard functions
will just work out of the box. (on glibc, they would require
-D_FILE_OFFSET_BITS=64 to work.) however, some programs instead define
_LARGEFILE64_SOURCE and use alternate versions of all the standard
types and functions with "64" appended to their names.
we do not want code to actually get linked against these functions
(it's ugly and inconsistent), so macros are used instead of prototypes
with weak aliases in the library itself. eventually the weak aliases
may be added at the library level for the sake of using code that was
originally built against glibc, but the macros will still be the
desired solution in the headers.
fcntl values 1024 and up are universal, arch-independent. later I'll
add some of the other linux-specific ones for notify, leases, pipe
size, etc. here too.
Jonathan Neuschäfer
Khem Raj
Szabolcs Nagy
Duncan Overbruck
Rich Felker
rofl0r