[Libguestfs] [nbdkit PATCH v2 03/17] server: Add utility functions for setting CLOEXEC and NONBLOCK

[Eric Blake]

Upcoming patches will be setting FD_CLOEXEC and/or O_NONBLOCK on more
files; the correct way to do this requires a read-modify-write, which
is enough lines of code to be worth a helper function.  I chose the
semantics of close()ing the fd on (unlikely) failure, on the grounds
that these functions will likely be used only immediately after the fd
is created.

Signed-off-by: Eric Blake <eblake at redhat.com>
---
 common/utils/utils.h |  2 ++
 common/utils/utils.c | 46 ++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 48 insertions(+)

diff --git a/common/utils/utils.h b/common/utils/utils.h
index 3f10cdc0..ebd5f66b 100644
--- a/common/utils/utils.h
+++ b/common/utils/utils.h
@@ -36,5 +36,7 @@
 extern void shell_quote (const char *str, FILE *fp);
 extern void uri_quote (const char *str, FILE *fp);
 extern int exit_status_to_nbd_error (int status, const char *cmd);
+extern int set_cloexec (int fd);
+extern int set_nonblock (int fd);

 #endif /* NBDKIT_UTILS_H */
diff --git a/common/utils/utils.c b/common/utils/utils.c
index 7534a13d..37c81871 100644
--- a/common/utils/utils.c
+++ b/common/utils/utils.c
@@ -32,11 +32,13 @@

 #include <config.h>

+#include <fcntl.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include <sys/types.h>
 #include <sys/wait.h>
+#include <unistd.h>

 #include <nbdkit-plugin.h>

@@ -126,3 +128,47 @@ exit_status_to_nbd_error (int status, const char *cmd)

   return 0;
 }
+
+/* Set the FD_CLOEXEC flag on the given fd, if it is non-negative.
+ * On failure, close fd and return -1; on success, return fd.
+ */
+int
+set_cloexec (int fd) {
+  int f;
+  int err;
+
+  if (fd == -1)
+    return -1;
+
+  f = fcntl (fd, F_GETFD);
+  if (f == -1 || fcntl (fd, F_SETFD, f | FD_CLOEXEC) == -1) {
+    err = errno;
+    nbdkit_error ("fcntl: %m");
+    close (fd);
+    errno = err;
+    return -1;
+  }
+  return fd;
+}
+
+/* Set the O_NONBLOCK flag on the given fd, if it is non-negative.
+ * On failure, close fd and return -1; on success, return fd.
+ */
+int
+set_nonblock (int fd) {
+  int f;
+  int err;
+
+  if (fd == -1)
+    return -1;
+
+  f = fcntl (fd, F_GETFL);
+  if (f == -1 || fcntl (fd, F_SETFL, f | O_NONBLOCK) == -1) {
+    err = errno;
+    nbdkit_error ("fcntl: %m");
+    close (fd);
+    errno = err;
+    return -1;
+  }
+  return fd;
+}
-- 
2.20.1