Attachment 248501 Details for Bug 273230 – manual page

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mq_getfd_np.2 (text/plain), 4.05 KB, created by unitrunker on 2024-02-16 09:08:44 UTC

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>.\" Copyright (c) 2024 Rick Parrish <unitrunker@unitrunker.net>
>.\"
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>.\" Portable Operating System Interface (POSIX), The Open Group Base
>.\" Specifications Issue 6, Copyright (C) 2001-2004 by the Institute of
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>.Dd February 16, 2024
>.Dt MQ_GETFD_NP 2
>.Os
>.Sh NAME
>.Nm mq_getfd_np
>.Nd "get a file descriptor on an open message queue descriptor"
>.Sh LIBRARY
>.Lb librt
>.Sh SYNOPSIS
>.In mqueue.h
>.Ft int
>.Fn mq_getfd_np "mqd_t mqd"
>.Sh DESCRIPTION
>The
>.Fn mq_getfd_np
>retrieves the underlying file descriptor from the given message queue descriptor
>returned from 
>.Xr mq_open 2 .
>The file descriptor is used by other functions to refer to that message queue.
>
>The
>.Fa mqd
>argument must be an open message queue descriptor.
>.Sh NOTES
>.Fx
>implements retrieval or alteration of message queue attributes based on file 
>descriptor.
>An open file descriptor is inherited by child after
>.Xr fork 2 .
>The file descriptor is closed in a new image after
>.Xr exec 3 .
>The
>.Xr fstat 2 ,
>.Xr fchmod 2 ,
>and
>.Xr fchown 2
>system calls are supported for file descriptor.
>.Pp
>Do not call
>.Xr close 2
>on the file descriptor. Instead, call
>.Xr mq_close 2
>on the mqd_t descriptor returned by 
>.Xr mq_open 2 .
>Do not use the file descriptor after calling 
>.Xr mq_close 2 .
>At best, file operations on the file descriptor will fail with
>.Xr errno 2
>set to EBADF (Bad file descriptor) error. 
>Worst case, the descriptor may be reused and now refers to a wholly different
>file or device.
>The file descriptor is safe to use so long as the message queue descriptor
>remains open.
>.Pp
>Please see the
>.Xr mqueuefs 5
>man page for instructions on loading the module or compiling the service into
>the kernel.
>.Sh RETURN VALUES
>Upon successful completion, the function returns a file descriptor; otherwise,
>an invalid file descriptor may be returned.
>.Sh ERRORS
>The
>.Fn mq_getfd_np
>system call does not return any errors but may cause SIGSEGV on an invalid
>message queue descriptor.
>.Sh SEE ALSO
>.Xr mq_close 2 ,
>.Xr mq_getattr 2 ,
>.Xr mq_open 2 ,
>.Xr mq_receive 2 ,
>.Xr mq_send 2 ,
>.Xr mq_setattr 2 ,
>.Xr mq_timedreceive 3 ,
>.Xr mq_timedsend 3 ,
>.Xr mq_unlink 2 ,
>.Xr mqueuefs 5
>.Sh HISTORY
>Support for mq_getdf_np first appeared in
>.Fx 11.0 .

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