common/man/preroot.3

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.aF 5 \\n(.f "\\$1" "\\$2" "\\$3" "\\$4" "\\$5" "\\$6" "\\$7"
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.aF 5 1 "\\$1" "\\$2" "\\$3" "\\$4" "\\$5" "\\$6" "\\$7"
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.aF 1 5 "\\$1" "\\$2" "\\$3" "\\$4" "\\$5" "\\$6" "\\$7"
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 PREROOT 3
 NAME
preroot - preroot support
 SYNOPSIS
.EX
#include <preroot.h>

char* getpreroot(char* path, char* cmd);
int ispreroot(char* dir);
int realopen(char* path, int mode, int perm);
void setpreroot(char** argv, char* dir);

 DESCRIPTION
The
 preroot routines manipulate the process preroot.
 preroot is a kernel supported per-process two level viewpath.
All pathnames rooted at
.L /
are first searched for in the process preroot directory
and then in the system root directory.
Setting the process preroot is a priveleged operation controlled by the
 /etc/preroot (1) command.

.L <preroot.h>
defines the symbol
 FS_PREROOT for those systems that support preroot.
The following routines are valid only when
 FS_PREROOT is defined:

.L getpreroot
returns a pointer to the absolute pathname of the preroot directory
for the executable
 cmd . The result is placed in
 path . If
 path is
 0 then
 malloc (3) is used to allocate the pathname space.
 0 is returned if
 cmd has no preroot or if an error was encountered.
In this case
 errno is set to indicate the error.

.L ispreroot
Non-zero is returned if
 dir is the current process preroot.
If
 dir is
 0 then non-zero is returned if the current process has a preroot.

.L realopen
temporarily disables the process preroot and does an
 open (3) relative to the system root directory.
The return value from
 open is returned.
If there is no preroot then
 realopen is equivalent to
 open .
.L setpreroot
calls
 execvp (3) as
.L "execvp(argv[0],argv)"
with the process preroot set to
 dir .  argv must be a
 0 -terminated argument array.
If
 argv is
 0 then the value of
 opt_argv from
 optget (3) is used.
.L setpreroot
returns immediately if
 dir is already the process preroot.
 "SEE ALSO"
/etc/preroot(1)
 BUGS
Preroot semantics should be preserved when reading directories.
The
 ast  directory (3) routines do this.
 3d (1) viewpathing does
 preroot the right way.