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b388e223f2
mi_switch(9) is still wildly innacurate. I suggest that every kernel developer takes 20 minutes a day for the next few days and updates one or two of his favourite chapter 9 man pages as they are now WAY out of date in general. I will add a couple of KSE related pages soon.
161 lines
4.3 KiB
Groff
161 lines
4.3 KiB
Groff
.\"
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.\" Copyright (C) 2001 Chad David <davidc@acns.ab.ca>. 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(s), this list of conditions and the following disclaimer as
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.\" the first lines of this file unmodified other than the possible
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.\" addition of one or more copyright notices.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice(s), 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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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``AS IS'' AND ANY
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.\" EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
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.\" WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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.\" DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE LIABLE FOR ANY
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.\" DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
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.\" (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
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.\" SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
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.\" 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 SUCH
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.\" DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd March 3, 2002
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.Dt UCRED 9
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.Os
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.Sh NAME
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.Nm ucred ,
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.Nm crget ,
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.Nm crhold ,
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.Nm crfree ,
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.Nm crshared ,
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.Nm crcopy ,
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.Nm crdup ,
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.Nm cru2x ,
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.NM cred_update_thread
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.Nd "functions related to user credentials"
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.Sh SYNOPSIS
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.In sys/param.h
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.In sys/ucred.h
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.Ft "struct ucred *"
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.Fn crget void
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.Ft "struct ucred *"
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.Fn crhold "struct ucred *cr"
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.Ft void
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.Fn crfree "struct ucred *cr"
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.Ft int
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.Fn crshared "struct ucred *cr"
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.Ft void
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.Fn crcopy "struct ucred *dest" "struct ucred *src"
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.Ft "struct ucred *"
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.Fn crdup "struct ucred *cr"
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.Ft void
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.Fn cru2x "struct ucred *cr" "struct xucred *xcr"
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.Ft void
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.Fn cred_update_thread "struct thread *td"
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.Sh DESCRIPTION
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The
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.Nm
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family of functions is used to manage user credential structures
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.Pq Vt "struct ucred"
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within the kernel.
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.Pp
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The
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.Fn crget
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function allocates memory
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for a new structure, sets its reference count to 1, and
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initializes its lock.
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.Pp
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The
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.Fn crhold
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function increases the reference count on the credential.
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.Pp
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The
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.Fn crfree
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function decreases the reference count on the credential.
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If the count drops to 0, the storage for the structure is freed.
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.Pp
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The
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.Fn crshared
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function returns true if the credential is shared.
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A credential is considered to be shared if its reference
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count is greater than one.
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.Pp
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The
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.Fn crcopy
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function copies the contents of the source (template)
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credential into the destination template.
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The
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.Vt uidinfo
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structure within the destination is referenced
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by calling
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.Xr uihold 9 .
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.Pp
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The
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.Fn crdup
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function allocates memory for a new structure and copies the
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contents of
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.Fa cr
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into it.
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The actual copying is performed by
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.Fn crcopy .
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.Pp
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The
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.Fn cru2x
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function converts a
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.Vt ucred
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structure to an
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.Vt xucred
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structure.
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That is,
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it copies data from
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.Fa cr
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to
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.Fa xcr ;
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it ignores fields in the former that are not present in the latter
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(e.g.,
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.Va cr_uidinfo ) ,
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and appropriately sets fields in the latter that are not present in
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the former
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(e.g.,
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.Va cr_version ) .
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.Pp
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The
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.Fn cred_update_thread
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function sets the credentials of
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.Fa td
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to that of its process, freeing its old credential if required.
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.Sh RETURN VALUES
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.Fn crget ,
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.Fn crhold
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and
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.Fn crdup
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all return a pointer to a
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.Vt ucred
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structure.
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.Pp
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.Fn crshared
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returns 0 if the credential has a reference count greater than 1;
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otherwise, 1 is returned.
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.Sh USAGE NOTES
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In general in a system call,
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you should always use the
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.Vt ucred
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associated with the
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thread doing the work rather than that of the process attached to it,
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As that associated with the thread is guaranteed to be safely accessed
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under SMP, and will remain stable for the duration of the call, even
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in the face of a multithreaded application changing the process credentials
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from another thread.
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.Sh SEE ALSO
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.Xr uihold 9
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.Sh AUTHORS
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This man page was written by
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.An Chad David Aq davidc@acns.ab.ca .
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