Change gcore in order to get rid of the procfs accesses and use FreeBSD's

specific sysctls and ptrace interfaces.
This change switches a bit gcore POLA that is summarized here:
- now gcore can recognize threads within the process and handle dumps
  on thread-scope
- the process to be analyzed will be stopped during its gcore run
- gcore may not work with processes which are actively being analyzed
  by gdb or truss
- the ptrace interface may cause syscalls to return EINTR, thus
  interferring with signals handling within the process

Side note: <janitor task> the interface can be further lifted in order to
get rid of the very last procfs interfaces remnants and made more
suitable for copying with sysctl/ptrace interface </janitor task>.

Obtained from:	Sandvine Incorporated
Reviewed by:	emaste, rwatson
Sponsored by:	Sandvine Incorporated
MFC:		1 month

1 files changed, 9 insertions, 13 deletions

diff --git a/usr.bin/gcore/gcore.1 b/usr.bin/gcore/gcore.1
index 981e0be3b346..a5be26a3f4d6 100644
--- a/usr.bin/gcore/gcore.1
+++ b/usr.bin/gcore/gcore.1
@@ -32,7 +32,7 @@
 .\"	@(#)gcore.1	8.2 (Berkeley) 4/18/94
 .\" $FreeBSD$
 .\"
-.Dd April 18, 1994
+.Dd November 18, 2009
 .Dt GCORE 1
 .Os
 .Sh NAME
@@ -55,11 +55,6 @@ By default, the core is written to the file
 The process identifier,
 .Ar pid ,
 must be given on the command line.
-If no executable image is
-specified,
-.Nm
-will use
-.Dq Pa /proc/<pid>/file .
 .Pp
 The following options are available:
 .Bl -tag -width indent
@@ -80,8 +75,6 @@ The same effect can be achieved manually with
 .Bl -tag -width /var/log/messages -compact
 .It Pa core.<pid>
 the core image
-.It Pa /proc/<pid>/file
-the executable image
 .El
 .Sh HISTORY
 A
@@ -89,12 +82,15 @@ A
 utility appeared in
 .Bx 4.2 .
 .Sh BUGS
-Context switches or paging activity that occur while
+Because of the
+.Xr ptrace 2
+usage
 .Nm
-is running may cause the program to become confused.
-For best results, use
-.Fl s
-to temporarily stop the target process.
+may not work with processes which are actively investigated with
+.Xr truss 1
+or
+.Xr gdb 1 .
+Additionally, interruptable sleeps may exit with EINTR.
 .Pp
 The
 .Nm