26d4f5e969
A more elegant way of obtaining a name of a character device by its file descriptor on FreeBSD, is to use the FIODGNAME ioctl. Because a valid file descriptor implies a file descriptor is visible in /dev, it will always resolve a valid device name. I'm adding a more friendly wrapper for this ioctl, called fdevname(). It is a lot easier to use than devname() and also has better error handling. When a device name cannot be resolved, it will just return NULL instead of a generated device name that makes no sense. Discussed with: kib
116 lines
3.2 KiB
Groff
116 lines
3.2 KiB
Groff
.\" Copyright (c) 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 4. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)devname.3 8.2 (Berkeley) 4/29/95
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.\" $FreeBSD$
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.\"
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.Dd February 22, 2005
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.Dt DEVNAME 3
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.Os
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.Sh NAME
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.Nm devname
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.Nd "get device name"
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In sys/stat.h
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.In stdlib.h
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.Ft char *
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.Fn devname "dev_t dev" "mode_t type"
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.Ft char *
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.Fn devname_r "dev_t dev" "mode_t type" "char *buf" "int len"
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.Ft char *
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.Fn fdevname "int fd"
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.Ft char *
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.Fn fdevname_r "int fd" "char *buf" "int len"
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.Sh DESCRIPTION
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The
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.Fn devname
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function returns a pointer to the name of the block or character
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device in
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.Pa /dev
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with a device number of
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.Fa dev ,
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and a file type matching the one encoded in
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.Fa type
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which must be one of
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.Dv S_IFBLK
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or
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.Dv S_IFCHR .
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To find the right name,
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.Fn devname
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asks the kernel via the
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.Va kern.devname
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sysctl.
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If it is unable to come up with a suitable name,
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it will format the information encapsulated in
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.Fa dev
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and
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.Fa type
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in a human-readable format.
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.Pp
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The
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.Fn fdevname
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and
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.Fn fdevname_r
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function obtains the device name directly from a file descriptor
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pointing to a character device.
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If it is unable to come up with a suitable name, these functions will
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return a NULL pointer.
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.Pp
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.Fn devname
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and
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.Fn fdevname
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return the name stored in a static buffer which will be overwritten
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on subsequent calls.
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.Fn devname_r
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and
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.Fn fdevname_r
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take a buffer and length as argument to avoid this problem.
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.Sh EXAMPLES
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.Bd -literal -compact
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int fd;
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struct stat buf;
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char *name;
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fd = open("/dev/tun");
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fstat(fd, &buf);
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printf("devname is /dev/%s\en", devname(buf.st_rdev, S_IFCHR));
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printf("fdevname is /dev/%s\en", fdevname(fd));
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.Ed
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.Sh SEE ALSO
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.Xr stat 2
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.Sh HISTORY
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The
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.Fn devname
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function appeared in
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.Bx 4.4 .
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The
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.Fn fdevname
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function appeared in
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.Fx 8.0 .
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