Hi,
The alignment text for O_DIRECT is slightly misleading:
Under Linux 2.4, transfer sizes, and the alignment of the user buffer
and the file offset must all be multiples of the logical block size of
the file system. Under Linux 2.6, alignment to 512-byte boundaries
suffices.
The last sentence is incorrect. You cannot perform O_DIRECT I/O in
sizes smaller than the underlying logical block size (for block devices
and block-based file systems; nfs is a different beast). I've attached
my proposed change. Comments and word-smithing are most welcome.
Cheers,
Jeff
Signed-off-by: Jeff Moyer <jmoyer@xxxxxxxxxx>
diff --git a/man2/open.2 b/man2/open.2
index e518c1f..df92d6a 100644
--- a/man2/open.2
+++ b/man2/open.2
@@ -787,7 +787,8 @@ operation in
Under Linux 2.4, transfer sizes, and the alignment of the user buffer
and the file offset must all be multiples of the logical block size
of the file system.
-Under Linux 2.6, alignment to 512-byte boundaries suffices.
+Under Linux 2.6, alignment to the underlying block device's logical
+block size suffices.
.LP
.B O_DIRECT
I/Os should never be run concurrently with the
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