[git commit master] Add FAQ entry about touching .config

[Denys Vlasenko]

commit: http://git.busybox.net/busybox-website/commit/?id=db5fdd14200585f9bddfb30e28a711c2e3e2195e
branch: http://git.busybox.net/busybox-website/commit/?id=refs/heads/master

Signed-off-by: Denys Vlasenko <vda.linux at googlemail.com>
---
 FAQ.html |   17 ++++++++++++++++-
 1 files changed, 16 insertions(+), 1 deletions(-)

diff --git a/FAQ.html b/FAQ.html
index 452aaa3..c5cf206 100644
--- a/FAQ.html
+++ b/FAQ.html
@@ -29,6 +29,7 @@ have additions to this FAQ document, we would love to add them,
 <li><a href="#init">Busybox init isn't working!</a></li>
 <li><a href="#sed">I can't configure busybox on my system.</a></li>
 <li><a href="#job_control">Why do I keep getting "sh: can't access tty; job control turned off" errors?  Why doesn't Control-C work within my shell?</a></li>
+<li><a href="#touch_config">sed "/CONFIG_FOO/s/.*/CONFIG_FOO=y/" -i .config; make; does not enable applet foo</a></li>
 </ol>
 
 <h2>Misc. questions</h2>
@@ -42,7 +43,7 @@ have additions to this FAQ document, we would love to add them,
   <li><a href="#design">What is the design of busybox?</a></li>
   <li><a href="#source">How is the source code organized?</a>
     <ul>
-    <li><a href="#source_applets">The applet directories.</a></li>
+    <li><a href="#source_applets">The applet directories</a></li>
     <li><a href="#source_libbb">The busybox shared library (libbb)</a></li>
     </ul>
   </li>
@@ -502,6 +503,20 @@ int main(int argc, char *argv)
 </p>
 
 <hr />
+<h2><a name="touch_config">sed "/CONFIG_FOO/s/.*/CONFIG_FOO=y/" -i .config; make; does not enable applet foo</a></h2>
+
+<p>
+    In some common cases like "make allnoconfig", both .config and dependent
+    generated files are updated, making their mtimes very close. If you have
+    a build script which modifies .config immediately after this,
+    and then rebuilds the busybox, it may happen that .config's mtime will be
+    still close the the generated files' mtimes. If filesystem
+    time granularity is low (for example, 1 second), these mtimes may end up
+    being equal, and dependent files wouldn't be rebuilt. The work around
+    is to add "sleep 1" before sed.
+</p>
+
+<hr />
 <h1>Misc. questions</h1>
 
 <hr />
-- 
1.6.3.3