From ecb81ae24786a0da0461a7718ee21c164fa5b9a2 Mon Sep 17 00:00:00 2001
From: James Stone <js@realm.io>
Date: Thu, 19 Oct 2017 14:20:23 -0700
Subject: [PATCH] Make posix_fallocate robust against interruption, report
 right errors

---
 CHANGELOG.md            |  4 +++-
 src/realm/util/file.cpp | 16 ++++++++++++----
 2 files changed, 15 insertions(+), 5 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 35c197f2602..304173402b3 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,7 +2,9 @@
 
 ### Bugfixes
 
-* Lorem ipsum.
+* Make calls to posix_fallocate() robust against interruption and report
+  the correct error on failure.
+  PR [#2905](https://github.com/realm/realm-core/pull/2905).
 
 ### Breaking changes
 
diff --git a/src/realm/util/file.cpp b/src/realm/util/file.cpp
index 4f7ba871c8c..5c16c3ce900 100644
--- a/src/realm/util/file.cpp
+++ b/src/realm/util/file.cpp
@@ -714,11 +714,19 @@ void File::prealloc_if_supported(SizeType offset, size_t size)
     if (int_cast_with_overflow_detect(size, size2))
         throw std::runtime_error("File size overflow");
 
-    if (::posix_fallocate(m_fd, offset, size2) == 0)
+    // posix_fallocate() does not set errno, it returns the error (if any) or zero.
+    // It is also possible for it to be interrupted by EINTR according to some man pages (ex fedora 24)
+    int status;
+    do {
+        status = ::posix_fallocate(m_fd, offset, size2);
+    } while (status == EINTR);
+
+    if (REALM_LIKELY(status == 0)) {
         return;
-    int err = errno; // Eliminate any risk of clobbering
-    std::string msg = get_errno_msg("posix_fallocate() failed: ", err);
-    if (err == ENOSPC || err == EDQUOT) {
+    }
+
+    std::string msg = get_errno_msg("posix_fallocate() failed: ", status);
+    if (status == ENOSPC || status == EDQUOT) {
         throw OutOfDiskSpace(msg);
     }
     throw std::runtime_error(msg);