shmop_open() can create or open a shared memory block.
Parameters
key
System's id for the shared memory block.
Can be passed as a decimal or hex.
flags
The flags that you can use:
"a" for access (sets SHM_RDONLY for shmat)
use this flag when you need to open an existing shared memory
segment for read only
"c" for create (sets IPC_CREATE)
use this flag when you need to create a new shared memory segment
or if a segment with the same key exists, try to open it for read
and write
"w" for read & write access
use this flag when you need to read and write to a shared memory
segment, use this flag in most cases.
"n" create a new memory segment (sets IPC_CREATE|IPC_EXCL)
use this flag when you want to create a new shared memory segment
but if one already exists with the same flag, fail. This is useful
for security purposes, using this you can prevent race condition
exploits.
mode
The permissions that you wish to assign to your memory segment, those
are the same as permission for a file. Permissions need to be passed
in octal form, like for example 0644
size
The size of the shared memory block you wish to create in bytes
Note:
Note: the 3rd and 4th should be entered as 0 if you are opening an
existing memory segment.
Return Values
On success shmop_open() will return an id that you can
use to access the shared memory segment you've created. FALSE is
returned on failure.