cursor/os-compatibility: handle EINTR gracefully

If os_resize_anonymous_file() called from os_create_anonymous_file()
fails with EINTR (Interrupted system call), then the buffer allocation
fails.

To avoid that, retry posix_fallocate() on EINTR.

However, in the presence of an alarm, the interrupt may trigger
repeatedly and prevent a large posix_fallocate() to ever complete
successfully, so we need to first block SIGALRM to prevent this.

Signed-off-by: Olivier Fourdan <ofourdan@redhat.com>

1 files changed, 20 insertions, 2 deletions

diff --git a/cursor/os-compatibility.c b/cursor/os-compatibility.c
index 07452a5..f2445ce 100644
--- a/cursor/os-compatibility.c
+++ b/cursor/os-compatibility.c
@@ -31,6 +31,7 @@
 #include <unistd.h>
 #include <fcntl.h>
 #include <errno.h>
+#include <signal.h>
 #include <string.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -168,11 +169,28 @@ int
 os_resize_anonymous_file(int fd, off_t size)
 {
 #ifdef HAVE_POSIX_FALLOCATE
+	sigset_t mask;
+	sigset_t old_mask;
+
+	/*
+	 * posix_fallocate() might be interrupted, so we need to check
+	 * for EINTR and retry in that case.
+	 * However, in the presence of an alarm, the interrupt may trigger
+	 * repeatedly and prevent a large posix_fallocate() to ever complete
+	 * successfully, so we need to first block SIGALRM to prevent
+	 * this.
+	 */
+	sigemptyset(&mask);
+	sigaddset(&mask, SIGALRM);
+	sigprocmask(SIG_BLOCK, &mask, &old_mask);
 	/*
-	 * Filesystems that do support fallocate will return EINVAL or
+	 * Filesystems that do not support fallocate will return EINVAL or
 	 * EOPNOTSUPP. In this case we need to fall back to ftruncate
 	 */
-	errno = posix_fallocate(fd, 0, size);
+	do {
+		errno = posix_fallocate(fd, 0, size);
+	} while (errno == EINTR);
+	sigprocmask(SIG_SETMASK, &old_mask, NULL);
 	if (errno == 0)
 		return 0;
 	else if (errno != EINVAL && errno != EOPNOTSUPP)