c++ - Access mmap memory from another process -

i've started playing mmap. i'm trying create example workspace extended real case.

this want achieve:

process 1:

• mmap file (actually device, it's okay generate example text file)

process 2: (not foked process 1; independent process)

• read memory mapped process 1
• change bits
• write new file

i've read several examples , documentations, still didn't find how achieve this. i'm missing is:

• how can process 2 access memory mapped process 1, without knowing opened file?
• how can put mmap content in new file? suppose have ftruncate new file, mmap file , memcpy content of process 1 memory map process 2 memory map (then msync)

side info, have message queue opened between 2 processes, can share messages if needed (ex. memory address/size, ...).

any hints?

thanks in advance!

mix

this answer considers trying stuff on linux/unix.

how can process 2 access memory mapped process 1, without knowing opened file?

process 1 passes mmap[1] flag map_shared.

you can:

• a) share file descriptor using unix domain sockets[2].
• b) send name of file using queues mentioned @ end of message.

process 2 opens mmap flag map_shared. modifications mmaped memory in process 1 visible process 2. if need fine control of when changes process 1 shown process 2 should control msync[3]

how can put mmap content in new file? suppose have ftruncate new file, mmap file , memcpy content of process 1 memory map process 2 memory map (then msync)

why don't write mmaped memory regular memory write?

[1]http://man7.org/linux/man-pages/man2/mmap.2.html

[2]portable way pass file descriptor between different processes

[3]http://man7.org/linux/man-pages/man2/msync.2.html