UBIFS: add new FAQ entry

Add FAQ entry: I see this UBIFS error: "validate_sb: LEB size
               mismatch: 129024 in superblock, 126976 real"

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>

diff --git a/faq/ubifs.xml b/faq/ubifs.xml
index c8993ea91a7594b99c2248eaa941fb0f82bf4a94..4056d8c6d4698949bcf1c98e0433842f7e9cb94e 100644 (file)
--- a/faq/ubifs.xml
+++ b/faq/ubifs.xml
@@ -34,6 +34,7 @@
        <li><a href="ubifs.html#L_empty_file">Why my file is empty after an unclean reboot?</a></li>
        <li><a href="ubifs.html#L_bgt_thread">What does the "ubifs_bgt0_0" thread do?</a></li>
        <li><a href="ubifs.html#L_sudden_ro">UBIFS suddenly became read-only - what is this?</a></li>
+       <li><a href="ubifs.html#L_lebsz_mismatch">I see this UBIFS error: "validate_sb: LEB size mismatch: 129024 in superblock, 126976 real"</a></li>
        <li><a href="ubifs.html#L_study_ubifs">I want to study UBIFS - any recommendations?</a></li>
 </ol>
 
@@ -966,6 +967,26 @@ an UBIFS bug, please, send a
 
 
 
+<h2><a name="L_lebsz_mismatch">
+I see this UBIFS error: "validate_sb: LEB size mismatch: 129024 in superblock, 126976 real"
+</a></h2>
+
+<p>When you create an UBIFS image using the <code>mkfs.ubifs</code> utility,
+you specify LEB size using the <code>-e</code> option. This is a very improtant
+parameter and you should specify it correctly in order to have working UBIFS
+image. Indeed, LEB size is the major UBIFS storage unit, e.g., UBIFS nodes
+never cross LEB boundaries, garbage collection is performed on individual LEBs,
+etc. See <a href="ubifs.html#L_mkfubifs">this</a> section for more
+information.</p>
+
+<p>The error message means that LEB size infromation which is stored in the
+UBIFS superblock does not match the real LEB size, which UBIFS takes from UBI.
+The superblock was created by the <code>mkfs.ubifs</code> utility, therefore
+you failed to pass the correct LEB size to the utility. Fix this by passing
+correct LEB size via the <code>-e</code> option.</p>
+
+
+
 <h2><a name="L_study_ubifs">I want to study UBIFS - any recommendations?</a></h2>
 
 <p>Follow <a href="../doc/ubifs.html#L_documentation">these</a> instructions.</p>