+++ /dev/null
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-.\" Kernel commit d97b46a64674a267bc41c9e16132ee2a98c3347d
-.\"
-.TH KCMP 2 2013-12-08 "Linux" "Linux Programmer's Manual"
-.SH NAME
-kcmp \- compare two processes to determine if they share a kernel resource
-.SH SYNOPSIS
-.nf
-.B #include <linux/kcmp.h>
-
-.BI "int kcmp(pid_t " pid1 ", pid_t " pid2 ", int " type ,
-.BI " unsigned long " idx1 ", unsigned long " idx2 );
-.fi
-
-.IR Note :
-There is no glibc wrapper for this system call; see NOTES.
-.SH DESCRIPTION
-The
-.BR kcmp ()
-system call can be used to check whether the two processes identified by
-.I pid1
-and
-.I pid2
-share a kernel resource such as virtual memory, file descriptors,
-and so on.
-
-The
-.I type
-argument specifies which resource is to be compared in the two processes.
-It has one of the following values:
-.TP
-.BR KCMP_FILE
-Check whether a file descriptor
-.I idx1
-in the process
-.I pid1
-refers to the same open file description (see
-.BR open (2))
-as file descriptor
-.I idx2
-in the process
-.IR pid2 .
-.TP
-.BR KCMP_FILES
-Check whether the process share the same set of open file descriptors.
-The arguments
-.I idx1
-and
-.I idx2
-are ignored.
-.TP
-.BR KCMP_FS
-Check whether the processes share the same filesystem information
-(i.e., file mode creation mask, working directory, and filesystem root).
-The arguments
-.I idx1
-and
-.I idx2
-are ignored.
-.TP
-.BR KCMP_IO
-Check whether the processes share I/O context.
-The arguments
-.I idx1
-and
-.I idx2
-are ignored.
-.TP
-.BR KCMP_SIGHAND
-Check whether the processes share the same table of signal dispositions.
-The arguments
-.I idx1
-and
-.I idx2
-are ignored.
-.TP
-.BR KCMP_SYSVSEM
-Check whether the processes share the same
-list of System\ V semaphore undo operations.
-The arguments
-.I idx1
-and
-.I idx2
-are ignored.
-.TP
-.BR KCMP_VM
-Check whether the processes share the same address space.
-The arguments
-.I idx1
-and
-.I idx2
-are ignored.
-.PP
-Note the
-.BR kcmp ()
-is not protected against false positives which may occur if tasks are
-running.
-One should stop tasks by sending
-.BR SIGSTOP
-(see
-.BR signal (7))
-prior to inspection with this system call to obtain meaningful results.
-.SH RETURN VALUE
-The return value of a successful call to
-.BR 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
-.I v1
-and
-.I v2
-are the addresses of appropriate resources, then the return value
-is one of the following:
-.RS 4
-.IP 0 4
-.I v1
-is equal to
-.IR v2 ;
-in other words, the two processes share the resource.
-.IP 1
-.I v1
-is less than
-.IR v2 .
-.IP 2
-.I v1
-is greater than
-.IR v2 .
-.IP 3
-.I v1
-is not equal to
-.IR v2 ,
-but ordering information is unavailable.
-.RE
-.PP
-On error, \-1 is returned, and
-.I errno
-is set appropriately.
-
-.BR kcmp ()
-was designed to return values suitable for sorting.
-This is particularly handy if one needs to compare
-a large number of file descriptors.
-.SH ERRORS
-.TP
-.B EBADF
-.I type
-is
-.B KCMP_FILE
-and
-.I fd1
-or
-.I fd2
-is not an open file descriptor.
-.TP
-.B EINVAL
-.I type
-is invalid.
-.TP
-.B EPERM
-Insufficient permission to inspect process resources.
-The
-.B CAP_SYS_PTRACE
-capability is required to inspect processes that you do not own.
-.TP
-.B ESRCH
-Process
-.I pid1
-or
-.I pid2
-does not exist.
-.SH VERSIONS
-The
-.BR kcmp ()
-system call first appeared in Linux 3.5.
-.SH CONFORMING TO
-.BR kcmp ()
-is Linux-specific and should not be used in programs intended to be portable.
-.SH NOTES
-Glibc does not provide a wrapper for this system call; call it using
-.BR syscall (2).
-
-This system call is available only if the kernel was configured with
-.BR 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
-.BR proc (5)
-filesystem; this was deemed to be unsuitable for security reasons.
-
-See
-.BR clone (2)
-for some background information on the shared resources
-referred to on this page.
-.SH SEE ALSO
-.BR clone (2),
-.BR unshare (2)
-.SH COLOPHON
-This page is part of release 3.79 of the Linux
-.I man-pages
-project.
-A description of the project,
-information about reporting bugs,
-and the latest version of this page,
-can be found at
-\%http://www.kernel.org/doc/man\-pages/.
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