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From e814f4b04ee413a7bb3dfa43e74c8fb4abf58359 Mon Sep 17 00:00:00 2001
From: Adhemerval Zanella <adhemerval.zanella@linaro.org>
Date: Tue, 24 Aug 2021 16:12:24 -0300
Subject: [PATCH] support: Add support_open_dev_null_range
It returns a range of file descriptor referring to the '/dev/null'
pathname. The function takes care of restarting the open range
if a file descriptor is found within the specified range and
also increases RLIMIT_NOFILE if required.
Checked on x86_64-linux-gnu.
---
support/Makefile | 2 +
support/support-open-dev-null-range.c | 134 ++++++++++++++++++++++++++
support/support.h | 8 ++
support/tst-support-open-dev-null-range.c | 155 ++++++++++++++++++++++++++++++
4 files changed, 299 insertions(+)
create mode 100644 support/support-open-dev-null-range.c
create mode 100644 support/tst-support-open-dev-null-range.c
diff --git a/support/Makefile b/support/Makefile
index a462781..6332e7b 100644
--- a/support/Makefile
+++ b/support/Makefile
@@ -66,6 +66,7 @@ libsupport-routines = \
support_path_support_time64 \
support_process_state \
support_ptrace \
+ support-open-dev-null-range \
support_openpty \
support_paths \
support_quote_blob \
@@ -264,6 +265,7 @@ tests = \
tst-support_capture_subprocess \
tst-support_descriptors \
tst-support_format_dns_packet \
+ tst-support-open-dev-null-range \
tst-support-process_state \
tst-support_quote_blob \
tst-support_quote_string \
diff --git a/support/support-open-dev-null-range.c b/support/support-open-dev-null-range.c
new file mode 100644
index 0000000..80d9dba
--- /dev/null
+++ b/support/support-open-dev-null-range.c
@@ -0,0 +1,134 @@
+/* Return a range of open file descriptors.
+ Copyright (C) 2021 Free Software Foundation, Inc.
+ This file is part of the GNU C Library.
+
+ The GNU C Library is free software; you can redistribute it and/or
+ modify it under the terms of the GNU Lesser General Public
+ License as published by the Free Software Foundation; either
+ version 2.1 of the License, or (at your option) any later version.
+
+ The GNU C Library is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public
+ License along with the GNU C Library; if not, see
+ <https://www.gnu.org/licenses/>. */
+
+#include <errno.h>
+#include <fcntl.h>
+#include <support/support.h>
+#include <support/check.h>
+#include <support/xunistd.h>
+#include <stdlib.h>
+#include <sys/resource.h>
+
+static void
+increase_nofile (void)
+{
+ struct rlimit rl;
+ if (getrlimit (RLIMIT_NOFILE, &rl) == -1)
+ FAIL_EXIT1 ("getrlimit (RLIMIT_NOFILE): %m");
+
+ rl.rlim_cur += 128;
+
+ if (setrlimit (RLIMIT_NOFILE, &rl) == 1)
+ FAIL_EXIT1 ("setrlimit (RLIMIT_NOFILE): %m");
+}
+
+static int
+open_dev_null (int flags, mode_t mode)
+{
+ int fd = open64 ("/dev/null", flags, mode);
+ if (fd > 0)
+ return fd;
+
+ if (fd < 0 && errno != EMFILE)
+ FAIL_EXIT1 ("open64 (\"/dev/null\", 0x%x, 0%o): %m", flags, mode);
+
+ increase_nofile ();
+
+ return xopen ("/dev/null", flags, mode);
+}
+
+struct range
+{
+ int lowfd;
+ size_t len;
+};
+
+struct range_list
+{
+ size_t total;
+ size_t used;
+ struct range *ranges;
+};
+
+static void
+range_init (struct range_list *r)
+{
+ r->total = 8;
+ r->used = 0;
+ r->ranges = xmalloc (r->total * sizeof (struct range));
+}
+
+static void
+range_add (struct range_list *r, int lowfd, size_t len)
+{
+ if (r->used == r->total)
+ {
+ r->total *= 2;
+ r->ranges = xrealloc (r->ranges, r->total * sizeof (struct range));
+ }
+ r->ranges[r->used].lowfd = lowfd;
+ r->ranges[r->used].len = len;
+ r->used++;
+}
+
+static void
+range_close (struct range_list *r)
+{
+ for (size_t i = 0; i < r->used; i++)
+ {
+ int minfd = r->ranges[i].lowfd;
+ int maxfd = r->ranges[i].lowfd + r->ranges[i].len;
+ for (int fd = minfd; fd < maxfd; fd++)
+ xclose (fd);
+ }
+ free (r->ranges);
+}
+
+int
+support_open_dev_null_range (int num, int flags, mode_t mode)
+{
+ /* We keep track of the ranges that hit an already opened descriptor, so
+ we close them after we get a working range. */
+ struct range_list rl;
+ range_init (&rl);
+
+ int lowfd = open_dev_null (flags, mode);
+ int prevfd = lowfd;
+ while (true)
+ {
+ int i = 1;
+ for (; i < num; i++)
+ {
+ int fd = open_dev_null (flags, mode);
+ if (fd != lowfd + i)
+ {
+ range_add (&rl, lowfd, prevfd - lowfd + 1);
+
+ prevfd = lowfd = fd;
+ break;
+ }
+ prevfd = fd;
+ }
+ if (i == num)
+ break;
+ }
+
+ range_close (&rl);
+
+ return lowfd;
+}
diff --git a/support/support.h b/support/support.h
index 834dba9..e6911e1 100644
--- a/support/support.h
+++ b/support/support.h
@@ -193,6 +193,14 @@ struct support_stack support_stack_alloc (size_t size);
/* Deallocate the STACK. */
void support_stack_free (struct support_stack *stack);
+
+/* Create a range of NUM opened '/dev/null' file descriptors using FLAGS and
+ MODE. The function takes care of restarting the open range if a file
+ descriptor is found within the specified range and also increases
+ RLIMIT_NOFILE if required.
+ The returned value is the lowest file descriptor number. */
+int support_open_dev_null_range (int num, int flags, mode_t mode);
+
__END_DECLS
#endif /* SUPPORT_H */
diff --git a/support/tst-support-open-dev-null-range.c b/support/tst-support-open-dev-null-range.c
new file mode 100644
index 0000000..8e29def
--- /dev/null
+++ b/support/tst-support-open-dev-null-range.c
@@ -0,0 +1,155 @@
+/* Tests for support_open_dev_null_range.
+ Copyright (C) 2021 Free Software Foundation, Inc.
+ This file is part of the GNU C Library.
+
+ The GNU C Library is free software; you can redistribute it and/or
+ modify it under the terms of the GNU Lesser General Public
+ License as published by the Free Software Foundation; either
+ version 2.1 of the License, or (at your option) any later version.
+
+ The GNU C Library is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public
+ License along with the GNU C Library; if not, see
+ <https://www.gnu.org/licenses/>. */
+
+#include <errno.h>
+#include <dirent.h>
+#include <fcntl.h>
+#include <limits.h>
+#include <support/check.h>
+#include <support/support.h>
+#include <support/xunistd.h>
+#include <sys/resource.h>
+#include <stdlib.h>
+
+#ifndef PATH_MAX
+# define PATH_MAX 1024
+#endif
+
+#include <stdio.h>
+
+static void
+check_path (int fd)
+{
+ char *proc_fd_path = xasprintf ("/proc/self/fd/%d", fd);
+ char file_path[PATH_MAX];
+ ssize_t file_path_length
+ = readlink (proc_fd_path, file_path, sizeof (file_path));
+ free (proc_fd_path);
+ if (file_path_length < 0)
+ FAIL_EXIT1 ("readlink (%s, %p, %zu)", proc_fd_path, file_path,
+ sizeof (file_path));
+ file_path[file_path_length] = '\0';
+ TEST_COMPARE_STRING (file_path, "/dev/null");
+}
+
+static int
+number_of_opened_files (void)
+{
+ DIR *fds = opendir ("/proc/self/fd");
+ if (fds == NULL)
+ FAIL_EXIT1 ("opendir (\"/proc/self/fd\"): %m");
+
+ int r = 0;
+ while (true)
+ {
+ errno = 0;
+ struct dirent64 *e = readdir64 (fds);
+ if (e == NULL)
+ {
+ if (errno != 0)
+ FAIL_EXIT1 ("readdir: %m");
+ break;
+ }
+
+ if (e->d_name[0] == '.')
+ continue;
+
+ char *endptr;
+ long int fd = strtol (e->d_name, &endptr, 10);
+ if (*endptr != '\0' || fd < 0 || fd > INT_MAX)
+ FAIL_EXIT1 ("readdir: invalid file descriptor name: /proc/self/fd/%s",
+ e->d_name);
+
+ /* Skip the descriptor which is used to enumerate the
+ descriptors. */
+ if (fd == dirfd (fds))
+ continue;
+
+ r = r + 1;
+ }
+
+ closedir (fds);
+
+ return r;
+}
+
+static int
+do_test (void)
+{
+ const int nfds1 = 8;
+ int lowfd = support_open_dev_null_range (nfds1, O_RDONLY, 0600);
+ for (int i = 0; i < nfds1; i++)
+ {
+ TEST_VERIFY (fcntl (lowfd + i, F_GETFL) > -1);
+ check_path (lowfd + i);
+ }
+
+ /* create some gaps. */
+ xclose (lowfd + 1);
+ xclose (lowfd + 5);
+ xclose (lowfd + 6);
+
+ const int nfds2 = 16;
+ int lowfd2 = support_open_dev_null_range (nfds2, O_RDONLY, 0600);
+ for (int i = 0; i < nfds2; i++)
+ {
+ TEST_VERIFY (fcntl (lowfd2 + i, F_GETFL) > -1);
+ check_path (lowfd2 + i);
+ }
+
+ /* Decrease the maximum number of files. */
+ {
+ struct rlimit rl;
+ if (getrlimit (RLIMIT_NOFILE, &rl) == -1)
+ FAIL_EXIT1 ("getrlimit (RLIMIT_NOFILE): %m");
+
+ rl.rlim_cur = number_of_opened_files ();
+
+ if (setrlimit (RLIMIT_NOFILE, &rl) == 1)
+ FAIL_EXIT1 ("setrlimit (RLIMIT_NOFILE): %m");
+ }
+
+ const int nfds3 = 16;
+ int lowfd3 = support_open_dev_null_range (nfds3, O_RDONLY, 0600);
+ for (int i = 0; i < nfds3; i++)
+ {
+ TEST_VERIFY (fcntl (lowfd3 + i, F_GETFL) > -1);
+ check_path (lowfd3 + i);
+ }
+
+ /* create a lot of gaps to trigger the range extension. */
+ xclose (lowfd3 + 1);
+ xclose (lowfd3 + 3);
+ xclose (lowfd3 + 5);
+ xclose (lowfd3 + 7);
+ xclose (lowfd3 + 9);
+ xclose (lowfd3 + 11);
+ xclose (lowfd3 + 13);
+
+ const int nfds4 = 16;
+ int lowfd4 = support_open_dev_null_range (nfds4, O_RDONLY, 0600);
+ for (int i = 0; i < nfds4; i++)
+ {
+ TEST_VERIFY (fcntl (lowfd4 + i, F_GETFL) > -1);
+ check_path (lowfd4 + i);
+ }
+
+ return 0;
+}
+
+#include <support/test-driver.c>
--
1.8.3.1
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