From 2da6e40822cc98dd940c10caad7f1f93cae74466 Mon Sep 17 00:00:00 2001 From: Ben Pfaff Date: Fri, 3 Dec 2004 21:22:15 +0000 Subject: [PATCH] Clarifications. --- doc/filesys.texi | 13 +++++++++++++ 1 file changed, 13 insertions(+) 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 -- 2.30.2