[libvirt PATCH] src: use closefrom() for mass closing of FDs

Daniel P. Berrangé berrange at redhat.com
Fri Feb 7 16:03:51 UTC 2020


On FreeBSD 12 the default ulimit settings allow for 100,000
open file descriptors. As a result spawning processes in
libvirt is abominably slow. Fortunately FreeBSD has long
since provided a good solution in the form of closefrom(),
which closes all FDs equal to or larger than the specified
parameter.

Signed-off-by: Daniel P. Berrangé <berrange at redhat.com>
---
 src/util/vircommand.c | 60 ++++++++++++++++++++++++++++++++++++++++---
 tests/testutils.c     |  9 +++++++
 2 files changed, 66 insertions(+), 3 deletions(-)

diff --git a/src/util/vircommand.c b/src/util/vircommand.c
index 904a3023c5..764fb2fe43 100644
--- a/src/util/vircommand.c
+++ b/src/util/vircommand.c
@@ -494,6 +494,59 @@ virCommandMassCloseGetFDsGeneric(virCommandPtr cmd G_GNUC_UNUSED,
 }
 # endif /* !__linux__ */
 
+# ifdef __FreeBSD__
+
+static int
+virCommandMassClose(virCommandPtr cmd,
+                    int childin,
+                    int childout,
+                    int childerr)
+{
+    int lastfd = -1;
+    int fd = -1;
+
+    /*
+     * Two phases of closing.
+     *
+     * The first (inefficient) phase iterates over FDs,
+     * preserving certain FDs we need to pass down, and
+     * closing others. The number of iterations is bounded
+     * to the number of the biggest FD we need to preserve.
+     *
+     * The second (speedy) phase uses closefrom() to cull
+     * all remaining FDs in the process.
+     *
+     * Usually the first phase will be fairly quick only
+     * processing a handful of low FD numbers, and thus using
+     * closefrom() is a massive win for high ulimit() NFILES
+     * values.
+     */
+    lastfd = MAX(lastfd, childin);
+    lastfd = MAX(lastfd, childout);
+    lastfd = MAX(lastfd, childerr);
+
+    while (fd < cmd->npassfd)
+        lastfd = MAX(lastfd, cmd->passfd[fd].fd);
+
+    for (fd = 0; fd <= lastfd; fd++) {
+        if (fd == childin || fd == childout || fd == childerr)
+            continue;
+        if (!virCommandFDIsSet(cmd, fd)) {
+            int tmpfd = fd;
+            VIR_MASS_CLOSE(tmpfd);
+        } else if (virSetInherit(fd, true) < 0) {
+            virReportSystemError(errno, _("failed to preserve fd %d"), fd);
+            return -1;
+        }
+    }
+
+    closefrom(lastfd + 1);
+
+    return 0;
+}
+
+# else /* ! __FreeBSD__ */
+
 static int
 virCommandMassClose(virCommandPtr cmd,
                     int childin,
@@ -520,13 +573,13 @@ virCommandMassClose(virCommandPtr cmd,
     if (!(fds = virBitmapNew(openmax)))
         return -1;
 
-# ifdef __linux__
+#  ifdef __linux__
     if (virCommandMassCloseGetFDsLinux(cmd, fds) < 0)
         return -1;
-# else
+#  else
     if (virCommandMassCloseGetFDsGeneric(cmd, fds) < 0)
         return -1;
-# endif
+#  endif
 
     fd = virBitmapNextSetBit(fds, 2);
     for (; fd >= 0; fd = virBitmapNextSetBit(fds, fd)) {
@@ -544,6 +597,7 @@ virCommandMassClose(virCommandPtr cmd,
     return 0;
 }
 
+# endif /* ! __FreeBSD__ */
 
 /*
  * virExec:
diff --git a/tests/testutils.c b/tests/testutils.c
index 7b9a5ea05b..662203d707 100644
--- a/tests/testutils.c
+++ b/tests/testutils.c
@@ -333,8 +333,10 @@ static
 void virTestCaptureProgramExecChild(const char *const argv[],
                                     int pipefd)
 {
+# ifndef __FreeBSD__
     size_t i;
     int open_max;
+# endif /* ! __FreeBSD__ */
     int stdinfd = -1;
     const char *const env[] = {
         "LANG=C",
@@ -344,6 +346,7 @@ void virTestCaptureProgramExecChild(const char *const argv[],
     if ((stdinfd = open("/dev/null", O_RDONLY)) < 0)
         goto cleanup;
 
+# ifndef __FreeBSD__
     open_max = sysconf(_SC_OPEN_MAX);
     if (open_max < 0)
         goto cleanup;
@@ -356,6 +359,7 @@ void virTestCaptureProgramExecChild(const char *const argv[],
             VIR_FORCE_CLOSE(tmpfd);
         }
     }
+# endif /* __FreeBSD__ */
 
     if (dup2(stdinfd, STDIN_FILENO) != STDIN_FILENO)
         goto cleanup;
@@ -364,6 +368,11 @@ void virTestCaptureProgramExecChild(const char *const argv[],
     if (dup2(pipefd, STDERR_FILENO) != STDERR_FILENO)
         goto cleanup;
 
+# ifdef __FreeBSD__
+    closefrom(STDERR_FILENO);
+    stdinfd = pipefd = -1;
+# endif
+
     /* SUS is crazy here, hence the cast */
     execve(argv[0], (char *const*)argv, (char *const*)env);
 
-- 
2.24.1




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