Hello Cyrill, On Mon, Jul 23, 2012 at 12:15 AM, Cyrill Gorcunov <gorcunov@xxxxxxxxxx> wrote: > NAME > kcmp - compare if two processes do share a particular kernel resource Very late follow up on this page, sorry. You didn't provide a copyright or license for this page. Could you please supply that information. See http://www.kernel.org/doc/man-pages/licenses.html . Cheers, Michael > SYNOPSIS > #define _GNU_SOURCE /* See feature_test_macros(7) */ > #include <unistd.h> > #include <linux/kcmp.h> > #include <sys/syscall.h> /* For SYS_xxx definitions */ > > int syscall(__NR_kcmp, pid1, pid2, type, idx1, idx2); > > DESCRIPTION > kcmp() allows to find out if two processes identified by pid1 and pid2 > share kernel resources such as virtual memory, file descriptors, file system etc. > > The comparison type is one of the following > > KCMP_FILE determines whether a file descriptor idx1 in the first process > is the same as another descriptor idx2 in the second process > > KCMP_VM compares whether processes share address space > > KCMP_FILES compares the file descriptor arrays to see whether the processes > share all files > > KCMP_FS compares whether processes share the file system information (the current > umask, working directory, namespace root, etc) > > KCMP_SIGHAND compares whether processes share a signal handlers table > > KCMP_IO compares whether processes do share I/O context, used mainly for > block I/O scheduling > > KCMP_SYSVSEM compares the list of undo operations associated with SYSV semaphores > > 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. > > RETURN VALUE > kcmp was designed to return values suitable for sorting. This is particularly handy > when one have to compare a large number of file descriptors. > > The return value is merely a result of simple arithmetic comparison of kernel pointers > (when kernel compares resources, it uses their memory addresses). > > The easiest way to explain is to consider an example. Lets say v1 and v2 are the > addresses of appropriate resources, then the return value is one of the following > > 0 - v1 is equal to v2 , in other words we have a shared resource here > 1 - v1 is less than v2 > 2 - v1 is greater than v2 > 3 - v1 is not equal to but ordering information is unavailble. > > On error, -1 is returned, and errno is set appropriately. > > Signed-off-by: Cyrill Gorcunov <gorcunov@xxxxxxxxxx> > CC: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx> > CC: "H. Peter Anvin" <hpa@xxxxxxxxx> > CC: Pavel Emelyanov <xemul@xxxxxxxxxxxxx> > CC: Al Viro <viro@xxxxxxxxxxxxxxxxxx> > Signed-off-by: Cyrill Gorcunov <gorcunov@xxxxxxxxxx> > --- > man2/kcmp.2 | 113 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ > 1 files changed, 113 insertions(+), 0 deletions(-) > create mode 100644 man2/kcmp.2 > > diff --git a/man2/kcmp.2 b/man2/kcmp.2 > new file mode 100644 > index 0000000..5d2e9a3 > --- /dev/null > +++ b/man2/kcmp.2 > @@ -0,0 +1,113 @@ > +.TH KCMP 2 2012-02-01 "Linux" "Linux Programmer's Manual" > + > +.SH NAME > +kcmp \- compare if two processes do share a particular kernel resource > + > +.SH SYNOPSIS > +.nf > +.BR "#define _GNU_SOURCE" " /* See feature_test_macros(7) */" > +.B #include <unistd.h> > +.B #include <linux/kcmp.h> > +.BR "#include <sys/syscall.h> " "/* For SYS_xxx definitions */" > + > +.BI "int syscall(__NR_kcmp, pid1, pid2, type, idx1, idx2);" > +.fi > + > +.SH DESCRIPTION > + > +.BR kcmp () > +allows to find out if two processes identified by > +.I pid1 > +and > +.I pid2 > +share kernel resources such as virtual memory, file descriptors, file system etc. > + > +The comparison > +.I type > +is one of the following > + > +.BR KCMP_FILE > +determines whether a file descriptor > +.I idx1 > +in the first process is the same as another descriptor > +.I idx2 > +in the second process > + > +.BR KCMP_VM > +compares whether processes share address space > + > +.BR KCMP_FILES > +compares the file descriptor arrays to see whether the processes share all files > + > +.BR KCMP_FS > +compares whether processes share the file system information (the current umask, > +working directory, namespace root, etc) > + > +.BR KCMP_SIGHAND > +compares whether processes share a signal handlers table > + > +.BR KCMP_IO > +compares whether processes do share I/O context, > +used mainly for block I/O scheduling > + > +.BR KCMP_SYSVSEM > +compares the list of undo operations associated with SYSV semaphores > + > +Note the > +.BR 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. > + > +.SH "RETURN VALUE" > +.B kcmp > +was designed to return values suitable for sorting. > +This is particularly handy when one have to compare > +a large number of file descriptors. > + > +The return value is merely a result of simple arithmetic comparison > +of kernel pointers (when kernel compares resources, it uses their > +memory addresses). > + > +The easiest way to explain is to consider an example. > +Lets say > +.I v1 > +and > +.I v2 > +are the addresses of appropriate resources, then the return value > +is one of the following > + > +.B 0 > +\- > +.I v1 > +is equal to > +.IR v2 , > +in other words we have a shared resource here > + > +.B 1 > +\- > +.I v1 > +is less than > +.I v2 > + > +.B 2 > +\- > +.I v1 > +is greater than > +.I v2 > + > +.B 3 > +\- > +.I v1 > +is not equal to > +.IR v2 , > +but ordering information is unavailable. > + > +On error, \-1 is returned, and errno is set appropriately. > + > +.SH "CONFORMING TO" > +.BR kcmp () > +is Linux specific and should not be used in programs intended to be portable. > +.SH "SEE ALSO" > +.BR clone (2) > -- > 1.7.7.6 > -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Author of "The Linux Programming Interface"; http://man7.org/tlpi/ -- To unsubscribe from this list: send the line "unsubscribe linux-man" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
