fd: free old file descriptor tables when not shared
During the life of a process, new file descriptor tables may be allocated. When a new table is allocated, the old table is placed in a free list and held onto until all processes referencing them exit. When a new file descriptor table is allocated, the old file descriptor table can be freed when the current process has a single-thread and the file descriptor table is not being shared with any other processes. Reviewed by: kevans Approved by: kevans (mentor) Differential Revision: https://reviews.freebsd.org/D18617
This commit is contained in:
parent
0b19f90a43
commit
3c85ca21d1
Notes:
svn2git
2020-12-20 02:59:44 +00:00
svn path=/head/; revision=367927
@ -1801,8 +1801,12 @@ fdgrowtable(struct filedesc *fdp, int nfd)
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atomic_store_rel_ptr((volatile void *)&fdp->fd_files, (uintptr_t)ntable);
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/*
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* Do not free the old file table, as some threads may still
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* reference entries within it. Instead, place it on a freelist
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* Free the old file table when not shared by other threads or processes.
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* The old file table is considered to be shared when either are true:
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* - The process has more than one thread.
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* - The file descriptor table has been shared via fdshare().
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*
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* When shared, the old file table will be placed on a freelist
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* which will be processed when the struct filedesc is released.
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*
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* Note that if onfiles == NDFILE, we're dealing with the original
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@ -1810,10 +1814,14 @@ fdgrowtable(struct filedesc *fdp, int nfd)
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* which must not be freed.
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*/
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if (onfiles > NDFILE) {
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ft = (struct freetable *)&otable->fdt_ofiles[onfiles];
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fdp0 = (struct filedesc0 *)fdp;
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ft->ft_table = otable;
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SLIST_INSERT_HEAD(&fdp0->fd_free, ft, ft_next);
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if (curproc->p_numthreads == 1 && fdp->fd_refcnt == 1)
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free(otable, M_FILEDESC);
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else {
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ft = (struct freetable *)&otable->fdt_ofiles[onfiles];
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fdp0 = (struct filedesc0 *)fdp;
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ft->ft_table = otable;
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SLIST_INSERT_HEAD(&fdp0->fd_free, ft, ft_next);
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}
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}
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/*
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* The map does not have the same possibility of threads still
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@ -10,6 +10,7 @@ TESTSDIR= ${TESTSBASE}/sys/kern
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#ATF_TESTS_C+= kcov
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ATF_TESTS_C+= kern_copyin
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ATF_TESTS_C+= kern_descrip_test
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ATF_TESTS_C+= fdgrowtable_test
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ATF_TESTS_C+= kill_zombie
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ATF_TESTS_C+= ptrace_test
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TEST_METADATA.ptrace_test+= timeout="15"
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@ -46,6 +47,7 @@ LIBADD.ptrace_test+= pthread
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LIBADD.unix_seqpacket_test+= pthread
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LIBADD.kcov+= pthread
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LIBADD.sendfile_helper+= pthread
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LIBADD.fdgrowtable_test+= util pthread kvm procstat
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NETBSD_ATF_TESTS_C+= lockf_test
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NETBSD_ATF_TESTS_C+= mqueue_test
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267
tests/sys/kern/fdgrowtable_test.c
Normal file
267
tests/sys/kern/fdgrowtable_test.c
Normal file
@ -0,0 +1,267 @@
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/*-
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* SPDX-License-Identifier: BSD-2-Clause-FreeBSD
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*
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* Copyright (c) 2020 Rob Wing
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*/
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#include <sys/cdefs.h>
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__FBSDID("$FreeBSD$");
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#include <sys/param.h>
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#include <sys/filedesc.h>
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#include <sys/queue.h>
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#include <sys/sysctl.h>
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#include <sys/user.h>
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#include <sys/wait.h>
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#include <atf-c.h>
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#include <fcntl.h>
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#include <signal.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <unistd.h>
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/* linked libraries */
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#include <kvm.h>
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#include <libutil.h>
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#include <libprocstat.h>
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#include <pthread.h>
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/* test-case macro */
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#define AFILE "afile"
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/*
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* The following macros, struct freetable, struct fdescenttbl0
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* and struct filedesc0 are copied from sys/kern/kern_descrip.c
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*/
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#define NDFILE 20
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#define NDSLOTSIZE sizeof(NDSLOTTYPE)
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#define NDENTRIES (NDSLOTSIZE * __CHAR_BIT)
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#define NDSLOT(x) ((x) / NDENTRIES)
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#define NDBIT(x) ((NDSLOTTYPE)1 << ((x) % NDENTRIES))
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#define NDSLOTS(x) (((x) + NDENTRIES - 1) / NDENTRIES)
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struct freetable {
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struct fdescenttbl *ft_table;
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SLIST_ENTRY(freetable) ft_next;
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};
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struct fdescenttbl0 {
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int fdt_nfiles;
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struct filedescent fdt_ofiles[NDFILE];
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};
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struct filedesc0 {
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struct filedesc fd_fd;
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SLIST_HEAD(, freetable) fd_free;
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struct fdescenttbl0 fd_dfiles;
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NDSLOTTYPE fd_dmap[NDSLOTS(NDFILE)];
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};
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static void
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openfiles(int n)
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{
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int i, fd;
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ATF_REQUIRE((fd = open(AFILE, O_CREAT, 0644)) != -1);
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close(fd);
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for (i = 0; i < n; i++)
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ATF_REQUIRE((fd = open(AFILE, O_RDONLY, 0644)) != -1);
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}
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/*
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* Get a count of the old file descriptor tables on the freelist.
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*/
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static int
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old_tables(kvm_t *kd, struct kinfo_proc *kp)
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{
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struct filedesc0 fdp0;
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struct freetable *ft, tft;
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int counter;
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counter = 0;
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ATF_REQUIRE(kvm_read(kd, (unsigned long) kp->ki_fd, &fdp0, sizeof(fdp0)) > 0);
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SLIST_FOREACH(ft, &fdp0.fd_free, ft_next) {
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ATF_REQUIRE(kvm_read(kd, (unsigned long) ft, &tft, sizeof(tft)) > 0 );
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ft = &tft;
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counter++;
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}
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return (counter);
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}
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/*
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* The returning struct kinfo_proc stores kernel addresses that will be
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* used by kvm_read to retrieve information for the current process.
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*/
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static struct kinfo_proc *
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read_kinfo(kvm_t *kd)
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{
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struct kinfo_proc *kp;
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int procs_found;
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ATF_REQUIRE((kp = kvm_getprocs(kd, KERN_PROC_PID, (int) getpid(), &procs_found)) != NULL);
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ATF_REQUIRE(procs_found == 1);
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return (kp);
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}
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/*
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* Test a single threaded process that doesn't have a shared
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* file descriptor table. The old tables should be freed.
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*/
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ATF_TC(free_oldtables);
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ATF_TC_HEAD(free_oldtables, tc)
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{
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atf_tc_set_md_var(tc, "require.user", "root");
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}
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ATF_TC_BODY(free_oldtables, tc)
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{
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kvm_t *kd;
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struct kinfo_proc *kp;
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ATF_REQUIRE((kd = kvm_open(NULL, NULL, NULL, O_RDONLY, NULL)) != NULL);
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openfiles(128);
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kp = read_kinfo(kd);
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ATF_CHECK(old_tables(kd,kp) == 0);
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}
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static void *
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exec_thread(void *args)
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{
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for (;;)
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sleep(1);
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}
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/*
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* Test a process with two threads that doesn't have a shared file
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* descriptor table. The old tables should not be freed.
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*/
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ATF_TC(oldtables_shared_via_threads);
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ATF_TC_HEAD(oldtables_shared_via_threads, tc)
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{
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atf_tc_set_md_var(tc, "require.user", "root");
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}
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ATF_TC_BODY(oldtables_shared_via_threads, tc)
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{
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kvm_t *kd;
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struct kinfo_proc *kp;
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pthread_t thread;
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ATF_REQUIRE((kd = kvm_open(NULL, NULL, NULL, O_RDONLY, NULL)) != NULL);
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ATF_REQUIRE(pthread_create(&thread, NULL, exec_thread, NULL) == 0);
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openfiles(128);
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kp = read_kinfo(kd);
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ATF_CHECK(kp->ki_numthreads > 1);
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ATF_CHECK(old_tables(kd,kp) > 1);
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ATF_REQUIRE(pthread_cancel(thread) == 0);
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ATF_REQUIRE(pthread_join(thread, NULL) == 0);
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}
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/*
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* Get the reference count of a file descriptor table.
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*/
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static int
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filedesc_refcnt(kvm_t *kd, struct kinfo_proc *kp)
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{
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struct filedesc fdp;
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ATF_REQUIRE(kvm_read(kd, (unsigned long) kp->ki_fd, &fdp, sizeof(fdp)) > 0);
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return (fdp.fd_refcnt);
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}
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/*
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* Test a single threaded process that shares a file descriptor
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* table with another process. The old tables should not be freed.
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*/
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ATF_TC(oldtables_shared_via_process);
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ATF_TC_HEAD(oldtables_shared_via_process, tc)
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{
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atf_tc_set_md_var(tc, "require.user", "root");
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}
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ATF_TC_BODY(oldtables_shared_via_process, tc)
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{
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kvm_t *kd;
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struct kinfo_proc *kp;
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int status;
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pid_t child, wpid;
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ATF_REQUIRE((kd = kvm_open(NULL, NULL, NULL, O_RDONLY, NULL)) != NULL);
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/* share the file descriptor table */
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ATF_REQUIRE((child = rfork(RFPROC)) != -1);
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if (child == 0) {
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openfiles(128);
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raise(SIGSTOP);
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exit(127);
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}
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/* let parent process open some files too */
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openfiles(128);
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/* get current status of child */
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wpid = waitpid(child, &status, WUNTRACED);
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/* child should be stopped */
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ATF_REQUIRE(WIFSTOPPED(status));
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/*
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* We want to read kernel data
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* before the child exits
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* otherwise we'll lose a reference count
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* to the file descriptor table
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*/
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if (child != 0) {
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kp = read_kinfo(kd);
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ATF_CHECK(filedesc_refcnt(kd,kp) > 1);
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ATF_CHECK(old_tables(kd,kp) > 1);
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kill(child, SIGCONT);
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}
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/* child should have exited */
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wpid = waitpid(child, &status, 0);
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ATF_REQUIRE(WIFEXITED(status));
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ATF_REQUIRE(WEXITSTATUS(status) == 127);
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}
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ATF_TP_ADD_TCS(tp)
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{
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ATF_TP_ADD_TC(tp, free_oldtables);
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ATF_TP_ADD_TC(tp, oldtables_shared_via_threads);
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ATF_TP_ADD_TC(tp, oldtables_shared_via_process);
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return (atf_no_error());
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}
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