From 2bebc5d953641a17afd9637db9c79b4aa5912474 Mon Sep 17 00:00:00 2001
From: Andrea Mazzoleni <amadvance@gmail.com>
Date: Sun, 1 May 2016 18:11:55 +0200
Subject: [PATCH] Add fallocate in Windows and comment about its use

---
 cmdline/mingw.c  |  9 +++++++++
 cmdline/mingw.h  |  8 ++++++++
 cmdline/parity.c | 47 ++++++++++++++++++++++++++++++++++++-----------
 3 files changed, 53 insertions(+), 11 deletions(-)

diff --git a/cmdline/mingw.c b/cmdline/mingw.c
index 4d0b0d8e..554992af 100644
--- a/cmdline/mingw.c
+++ b/cmdline/mingw.c
@@ -904,6 +904,15 @@ int windows_ftruncate(int fd, off64_t off)
 	return 0;
 }
 
+int windows_fallocate(int fd, int mode, off64_t off, off64_t len)
+{
+	if (mode != 0)
+		return -1;
+
+	/* no difference with ftruncate because Windows doesn't use sparse files */
+	return windows_ftruncate(fd, off + len);
+}
+
 int windows_fsync(int fd)
 {
 	HANDLE h;
diff --git a/cmdline/mingw.h b/cmdline/mingw.h
index 6233b3dc..f36e4fe3 100644
--- a/cmdline/mingw.h
+++ b/cmdline/mingw.h
@@ -58,6 +58,9 @@
 #define HAVE_FTRUNCATE 1
 #undef ftruncate
 #define ftruncate windows_ftruncate
+#define HAVE_FALLOCATE 1
+#undef fallocate
+#define fallocate windows_fallocate
 #define HAVE_FSYNC 1
 #undef fsync
 #define fsync windows_fsync
@@ -207,6 +210,11 @@ int lstat_sync(const char* file, struct windows_stat* st, uint64_t* physical);
  */
 int windows_ftruncate(int fd, off64_t off);
 
+/**
+ * Like the C fallocate().
+ */
+int windows_fallocate(int fd, int mode, off64_t off, off64_t len);
+
 /**
  * Like the C fsync().
  */
diff --git a/cmdline/parity.c b/cmdline/parity.c
index b18b594a..cf726621 100644
--- a/cmdline/parity.c
+++ b/cmdline/parity.c
@@ -258,16 +258,32 @@ static int parity_handle_grow(struct snapraid_split_handle* split, data_off_t si
 
 #if HAVE_FALLOCATE
 	if (!skip_fallocate) {
-		/* allocate real space using the specific Linux fallocate() operation. */
-		/* If the underline file-system doesn't support it, this operation fails, */
-		/* instead posix_fallocate() fallbacks to write the whole file. */
+		/*
+		 * Allocate real space using the specific Linux fallocate() operation.
+		 * If the underline file-system doesn't support it, this operation fails.
+		 *
+		 * Instead posix_fallocate() fallbacks to write the whole file,
+		 * and we cannot use it as we may need to initialize a multi terabyte
+		 * file.
+		 *
+		 * See: fallocate vs posix_fallocate
+		 * http://stackoverflow.com/questions/14063046/fallocate-vs-posix-fallocate
+		 */
 		ret = fallocate(split->f, 0, 0, size);
 
-		/* fallocate() returns the error number as positive integer, */
-		/* and in this case it doesn't set errno, just like posix_fallocate() */
-		/* Checking the glibc code (2.11.1 and 2.14.1) it seems that ENOSYS */
-		/* may be returned in errno, so we support both the return way */
-		if (ret > 0) { /* if a positive error is returned, convert it to errno */
+		/*
+		 * In some legacy system fallocate() may return the error number
+		 * as  positive integer, and in this case it doesn't set errno.
+		 *
+		 * Detect and handle this case.
+		 *
+		 * See: Fix fallocate error return on i386
+		 * https://sourceware.org/ml/libc-hacker/2010-04/msg00000.html
+		 *
+		 * See: [PATCH XFS] Fix error return for fallocate() on XFS
+		 * http://oss.sgi.com/archives/xfs/2009-11/msg00201.html
+		 */
+		if (ret > 0) {
 			/* LCOV_EXCL_START */
 			errno = ret;
 			ret = -1;
@@ -278,9 +294,18 @@ static int parity_handle_grow(struct snapraid_split_handle* split, data_off_t si
 		ret = -1;
 	}
 
-	/* we get EOPNOTSUPP if the operation is not supported, like in ext3/ext2 */
-	/* or ENOSYS with kernel before 2.6.23 */
-	if (errno == EOPNOTSUPP || errno == ENOSYS) {
+	/*
+	 * Fallback to ftruncate() if the operation is not supported.
+	 *
+	 * We get EOPNOTSUPP if the operation is not supported, like in ext3/ext2
+	 * or ENOSYS with kernel before 2.6.23, because fallocate is not supported
+	 * at all.
+	 *
+	 * See: man fallocate
+	 * ENOSYS - This kernel does not implement fallocate().
+         * EOPNOTSUPP - The file system containing the file referred to by fd does not support this operation
+	 */
+	if (ret != 0 && (errno == EOPNOTSUPP || errno == ENOSYS)) {
 		/* fallback using ftruncate() */
 		ret = ftruncate(split->f, size);
 	}