Updated version based on feedback from John. --- >From ade1eba229b558431581448e7d7838f0e1fe2c49 Mon Sep 17 00:00:00 2001 From: Michal Hocko <mhocko@xxxxxxxx> Date: Wed, 29 Nov 2017 15:32:08 +0100 Subject: [PATCH] mmap.2: document new MAP_FIXED_SAFE flag 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 <jhubbard@xxxxxxxxxx>] Signed-off-by: Michal Hocko <mhocko@xxxxxxxx> --- man2/mmap.2 | 22 ++++++++++++++++++++++ 1 file changed, 22 insertions(+) diff --git a/man2/mmap.2 b/man2/mmap.2 index 385f3bfd5393..923bbb290875 100644 --- a/man2/mmap.2 +++ b/man2/mmap.2 @@ -225,6 +225,22 @@ will fail. Because requiring a fixed address for a mapping is less portable, the use of this option is discouraged. .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 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 @@ -449,6 +465,12 @@ 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 -- Michal Hocko SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
