From 637789d11b720c00ea7dace5cf9cbbb9229c48f8 Mon Sep 17 00:00:00 2001
From: Andrea Mazzoleni <amadvance@users.sourceforge.net>
Date: Tue, 29 Mar 2011 18:27:25 +0200
Subject: [PATCH] Some comments about the use of posix_advise().

---
 HISTORY  |  1 +
 handle.c |  8 ++++++++
 parity.c | 14 +++++++++++---
 3 files changed, 20 insertions(+), 3 deletions(-)

diff --git a/HISTORY b/HISTORY
index 9d50d37e..1bbc32fe 100644
--- a/HISTORY
+++ b/HISTORY
@@ -3,6 +3,7 @@ SnapRAID HISTORY
 
 0.3 2011/4
 ==========
+* Better ETA estimation.
 * Added support for OpenSSL crypto library to use its optimized MD5 implementation.
 * Added test vector for MD5.
 * Added a speed test option for MD5.
diff --git a/handle.c b/handle.c
index c65b6536..851b559f 100644
--- a/handle.c
+++ b/handle.c
@@ -256,6 +256,11 @@ int handle_read(struct snapraid_handle* handle, struct snapraid_block* block, un
 		return -1;
 	}
 
+	/* Here isn't needed to call posix_fadvise(..., POSIX_FADV_DONTNEED) because */
+	/* we already advised sequential access with POSIX_FADV_SEQUENTIAL. */
+	/* In Linux 2.6.33 it's enough to ensure that data is not kept in the cache. */
+	/* Better to do nothing and save a syscall for each block. */
+
 	return read_size;
 }
 
@@ -284,6 +289,9 @@ int handle_write(struct snapraid_handle* handle, struct snapraid_block* block, u
 		return -1;
 	}
 
+	/* Here doesn't make sense to call posix_fadvise(..., POSIX_FADV_DONTNEED) because */
+	/* at this time the data is still in not yet written and it cannot be discharged. */
+
 	return 0;
 }
 
diff --git a/parity.c b/parity.c
index 05c76bf9..e4f85fd5 100644
--- a/parity.c
+++ b/parity.c
@@ -143,9 +143,9 @@ int parity_sync(const char* path, int f)
 #if HAVE_FSYNC
 	int ret;
 
-	/* ensure that data changes are written to disk */
-	/* this is required to ensure that parity is more updated than content */
-	/* in case of a system crash */
+	/* Ensure that data changes are written to disk. */
+	/* This is required to ensure that parity is more updated than content */
+	/* in case of a system crash. */
 	ret = fsync(f);
 	if (ret != 0) {
 		fprintf(stderr, "Error synching parity file '%s'. %s.\n", path, strerror(errno));
@@ -202,6 +202,9 @@ int parity_write(const char* path, int f, block_off_t pos, unsigned char* block_
 		return -1;
 	}
 
+	/* Here doesn't make sense to call posix_fadvise(..., POSIX_FADV_DONTNEED) because */
+	/* at this time the data is still in not yet written and it cannot be discharged. */
+
 	return 0;
 }
 
@@ -227,6 +230,11 @@ int parity_read(const char* path, int f, block_off_t pos, unsigned char* block_b
 		return -1;
 	}
 
+	/* Here isn't needed to call posix_fadvise(..., POSIX_FADV_DONTNEED) because */
+	/* we already advised sequential access with POSIX_FADV_SEQUENTIAL. */
+	/* In Linux 2.6.33 it's enough to ensure that data is not kept in the cache. */
+	/* Better to do nothing and save a syscall for each block. */
+
 	return block_size;
 }