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Questions about mmap and shm_open

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Top Forums Programming Questions about mmap and shm_open
# 8  
Old 12-05-2009
You know, it sounds like you need to use a database engine - Oracle, for example, makes extensive use of shared memory and huge in-memory caches of data. This is what it seems you are trying to implement:

Sharing a large data object across many processes.

Parenthetically - don't you find it odd that some really brilliant people have written world class applications using techiniques that you view as defective. There is your position, then there are 100K programmers, applications designers, OS developers - all of whom accept an opposite point of view. And one they have used for years.

When you read technical manual, you take what is said there on authority. Can you not do the same with mainstream unix programming practices? At least until you really know a lot more....

Corona has given you good advice. Take it or leave it.
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LEARN ABOUT SUSE

mmap64

MMAP2(2)						     Linux Programmer's Manual							  MMAP2(2)

NAME

       mmap2 - map files or devices into memory

SYNOPSIS

       #include <sys/mman.h>

       void *mmap2(void *addr, size_t length, int prot,
		    int flags, int fd, off_t pgoffset);

DESCRIPTION

       The  mmap2()  system call operates in exactly the same way as mmap(2), except that the final argument specifies the offset into the file in
       4096-byte units (instead of bytes, as is done by mmap(2)).  This enables applications that use a 32-bit off_t to map  large  files  (up	to
       2^44 bytes).

RETURN VALUE

       On success, mmap2() returns a pointer to the mapped area.  On error -1 is returned and errno is set appropriately.

ERRORS

       EFAULT Problem with getting the data from userspace.

       EINVAL (Various platforms where the page size is not 4096 bytes.)  offset * 4096 is not a multiple of the system page size.

       mmap2() can return any of the same errors as mmap(2).

VERSIONS

       mmap2() is available since Linux 2.3.31.

CONFORMING TO

       This system call is Linux-specific.

NOTES

       Nowadays, the glibc mmap() wrapper function invokes this system call rather than the mmap(2) system call.

       On ia64, the unit for offset is actually the system page size, rather than 4096 bytes.

SEE ALSO

       getpagesize(2), mmap(2), mremap(2), msync(2), shm_open(3)

COLOPHON

       This  page is part of release 3.25 of the Linux man-pages project.  A description of the project, and information about reporting bugs, can
       be found at http://www.kernel.org/doc/man-pages/.

Linux								    2008-04-22								  MMAP2(2)