linux-ext4 - Defrag and delayed-allocation on Ext4

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-ID: <CA+1E3r+hpUzPzeVT+TBMXN7VrQMfs6E56WPHGvnd4vD51uBgBg@mail.gmail.com>
Date:   Wed, 29 Aug 2018 21:52:32 +0530
From:   Joshi <joshiiitr@...il.com>
To:     linux-ext4@...r.kernel.org
Subject: Defrag and delayed-allocation on Ext4

Possibly a newbie question for the list, excuse my ignorance.
I saw e4defrag code, which fallocates a temporary file in the outset.

I imagine that extents would not get allocated to the this file at
this time due to delayed-allocation feature (extent/block allocations
should happen post writes which seem to happen much later, during
extents copying between target-file and temporary-file).

However, e4defrag needs extent information just after fallocate() to
determine whether it is wise to go-ahead with defrag process i.e.
whether new file is any less-fragmented than target one. I wonder how
this decision-making is possible if fallocate does not allocate
extents/blocks.

I'd appreciate the thoughts.

-- 
Joshi