kcmp — compare two processes to determine if they share a kernel resource
#include <linux/kcmp.h>
int
kcmp( |
pid_t pid1, |
| pid_t pid2, | |
| int type, | |
| unsigned long idx1, | |
unsigned long idx2); |
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Note |
|---|---|
| There is no glibc wrapper for this system call; see NOTES. |
The kcmp() system call can
be used to check whether the two processes identified by
pid1 and pid2 share a kernel resource
such as virtual memory, file descriptors, and so on.
The type argument
specifies which resource is to be compared in the two
processes. It has one of the following values:
KCMP_FILECheck whether a file descriptor idx1 in the process
pid1 refers to
the same open file description (see open(2)) as file
descriptor idx2
in the process pid2.
KCMP_FILESCheck whether the process share the same set of open
file descriptors. The arguments idx1 and idx2 are ignored.
KCMP_FSCheck whether the processes share the same file
system information (i.e., file mode creation mask,
working directory, and file system root). The arguments
idx1 and
idx2 are
ignored.
KCMP_IOCheck whether the processes share I/O context. The
arguments idx1
and idx2 are
ignored.
KCMP_SIGHANDCheck whether the processes share the same table of
signal dispositions. The arguments idx1 and idx2 are ignored.
KCMP_SYSVSEMCheck whether the processes share the same list of
System V semaphore undo operations. The arguments
idx1 and
idx2 are
ignored.
KCMP_VMCheck whether the processes share the same address
space. The arguments idx1 and idx2 are ignored.
Note the kcmp() is not
protected against false positives which may have place if
tasks are running. Which means one should stop tasks being
inspected with this syscall to obtain meaningful results.
The return value of a successful call to kcmp() is simply the result of arithmetic
comparison of kernel pointers (when the kernel compares
resources, it uses their memory addresses).
The easiest way to explain is to consider an example.
Suppose that v1 and
v2 are the
addresses of appropriate resources, then the return value is
one of the following:
0
v1is equal tov2; in other words, the two processes share the resource.1
v1is less thanv2.2
v1is greater thanv2.3
v1is not equal tov2, but ordering information is unavailable.
On error, −1 is returned, and errno is set appropriately.
kcmp () was designed to
return values suitable for sorting. This is particularly
handy if one needs to compare a large number of file
descriptors.
type is
KCMP_FILE and fd1 or fd2 is not an open file
descriptor.
type is
invalid.
Insufficient permission to inspect process
resources. The CAP_SYS_PTRACE capability is required
to inspect processes that you do not own.
Process pid1
or pid2 does
not exist.
Glibc does not provide a wrapper for this system call; call it using syscall(2).
This system call is available only if the kernel was
configured with CONFIG_CHECKPOINT_RESTORE. The main use of
the system call is for the checkpoint/restore in user space
(CRIU) feature. The alternative to this system call would
have been to expose suitable process information via the
proc(5) file system; this
was deemed to be unsuitable for security reasons.
See clone(2) for some background information on the shared resources referred to on this page.
This page is part of release 3.50 of the Linux man-pages project. A
description of the project, and information about reporting
bugs, can be found at
http://www.kernel.org/doc/man-pages/.
|
Copyright (C) 2012, Cyrill Gorcunov <gorcunovopenvz.org> and Copyright (C) 2012, Michael Kerrisk <mtk.manpagesgmail.com> %%%LICENSE_START(VERBATIM) Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Since the Linux kernel and libraries are constantly changing, this manual page may be incorrect or out-of-date. The author(s) assume. no responsibility for errors or omissions, or for damages resulting. from the use of the information contained herein. The author(s) may. not have taken the same level of care in the production of this. manual, which is licensed free of charge, as they might when working. professionally. Formatted or processed versions of this manual, if unaccompanied by the source, must acknowledge the copyright and authors of this work. %%%LICENSE_END Kernel commit d97b46a64674a267bc41c9e16132ee2a98c3347d |