From: Michal Hocko <mho...@suse.com> 4.16+ kernels offer a new MAP_FIXED_SAFE flag which allows the caller to atomicaly probe for a given address range.
[wording heavily updated by John Hubbard <jhubb...@nvidia.com>] Signed-off-by: Michal Hocko <mho...@suse.com> --- man2/mmap.2 | 22 ++++++++++++++++++++++ 1 file changed, 22 insertions(+) diff --git a/man2/mmap.2 b/man2/mmap.2 index a5a8eb47a263..02d391697ce6 100644 --- a/man2/mmap.2 +++ b/man2/mmap.2 @@ -227,6 +227,22 @@ in mind that the exact layout of a process' memory map is allowed to change significantly between kernel versions, C library versions, and operating system releases. .TP +.BR MAP_FIXED_SAFE " (since Linux 4.16)" +Similar to MAP_FIXED with respect to the +.I +addr +enforcement, but different in that MAP_FIXED_SAFE never clobbers a pre-existing +mapped range. If the requested range would collide with an existing +mapping, then this call fails with +.B EEXIST. +This flag can therefore be used as a way to atomically (with respect to other +threads) attempt to map an address range: one thread will succeed; all others +will report failure. Please note that older kernels which do not recognize this +flag will typically (upon detecting a collision with a pre-existing mapping) +fall back to a "non-MAP_FIXED" type of behavior: they will return an address that +is different than the requested one. Therefore, backward-compatible software +should check the returned address against the requested address. +.TP .B MAP_GROWSDOWN This flag is used for stacks. It indicates to the kernel virtual memory system that the mapping @@ -451,6 +467,12 @@ is not a valid file descriptor (and .B MAP_ANONYMOUS was not set). .TP +.B EEXIST +range covered by +.IR addr , +.IR length +is clashing with an existing mapping. +.TP .B EINVAL We don't like .IR addr , -- 2.15.0
