From: Ben Pfaff <blp@cs.stanford.edu>
Date: Fri, 3 Dec 2004 21:22:15 +0000 (+0000)
Subject: Clarifications.
X-Git-Url: https://pintos-os.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=2da6e40822cc98dd940c10caad7f1f93cae74466;p=pintos-anon

Clarifications.
---

diff --git a/doc/filesys.texi b/doc/filesys.texi
index 090397c..33cf740 100644
--- a/doc/filesys.texi
+++ b/doc/filesys.texi
@@ -111,6 +111,19 @@ root directory file to expand beyond its current limit of ten files.
 Make sure that concurrent accesses to the inode remain properly
 synchronized.
 
+The user is allowed to seek beyond the current end-of-file (EOF).  The
+seek itself does not extend the file.  Writing at a position past EOF
+extends the file to the position being written, and any gap between the
+previous EOF and the start of the write must be filled with zeros.  A
+read past EOF returns zero bytes.
+
+Writing far beyond EOF can cause many blocks to be entirely zero.  Some
+file systems allocate and write real data blocks for these implicitly
+zeroed blocks.  Other file systems do not allocate these blocks at all
+until they are explicitly written.  The latter file systems are said to
+support ``sparse files.''  You may adopt either allocation strategy in
+your file system.
+
 @node Problem 4-3 Subdirectories
 @section Problem 4-3: Subdirectories