Gary E. Miller <g...@rellim.com>: > ntpd, chronyd and gpsd use shmctl(2), the old SYSVr4 interface. > > The 'new' as of 2001 interface is shm_open(3). > > Both are in POSIX 2001 and POSIX 2008. > > man shm_overview has this to say: > > "System V shared memory (shmget(2), shmop(2), etc.) is an older > shared memory API. POSIX shared memory provides a simpler, and > better designed interface; on the other hand POSIX shared memory > is somewhat less widely available (especially on older systems) > than System V shared memory." > > In any case, they are not trivially interchangeable at the binary level. > So a refclock based on shm_open() would be a new refclock. IMHO it would > be slightly better than shmctl(), but I'd prefer to go all the way and fix > #48, skipping these intermediate steps.
I did not know this. Topic for investigation: can we write code using
the new interface that interoperates cleanly with the old one?
Looking at shm_overview it looks like this should be almost possible.
If I'm reading the tea leaves correctly, shm_open(2) returns a
shared-memory area with the access semantics of a file. The base
address of the segment is unavailable, and memcpy() operations have to
be replaced with read()/write(), but these are details.
The problem is we don't know what, if any, mapping is possible between
shmget segment keys and shopen filenames. Grr. There may not be one.
--
<a href="http://www.catb.org/~esr/";>Eric S. Raymond</a>
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