linux-ext4 - Regarding random grouop search start for allocation of inode.

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: <CAKJOkCrU7b3XLKHFUS-_eyZ9Lvh7XoPcU15pjAs+qGy2o6XA-w@mail.gmail.com>
Date:	Thu, 3 Dec 2015 13:14:37 +0530
From:	lokesh jaliminche <lokesh.jaliminche@...il.com>
To:	linux-ext4@...r.kernel.org
Subject: Regarding random grouop search start for allocation of inode.

hello folks,
                I am new to ext4 code. I was going through the
ext4-source for allocation of inode.
There is one thing that I did not understand while selection of groups
for inode allocation . I came across this code snippet which is part
of find_group_orlov function. question is, why group search start is
random ?

Code snippet:
==========
···if (qstr) {
»·······»·······»·······hinfo.hash_version = LDISKFS_DX_HASH_HALF_MD4;
»·······»·······»·······hinfo.seed = sbi->s_hash_seed;
»·······»·······»·······ldiskfsfs_dirhash(qstr->name, qstr->len, &hinfo);
»·······»·······»·······grp = hinfo.hash;
»·······»·······} else
»·······»·······»·······get_random_bytes(&grp, sizeof(grp));
»·······»·······parent_group = (unsigned)grp % ngroups;
»·······»·······for (i = 0; i < ngroups; i++) {
»·······»·······»·······g = (parent_group + i) % ngroups;
»·······»·······»·······get_orlov_stats(sb, g, flex_size, &stats);
»·······»·······»·······if (!stats.free_inodes)
»·······»·······»·······»·······continue;
»·······»·······»·······if (stats.used_dirs >= best_ndir)
»·······»·······»·······»·······continue;
»·······»·······»·······if (stats.free_inodes < avefreei)
»·······»·······»·······»·······continue;
»·······»·······»·······if (stats.free_blocks < avefreeb)
»·······»·······»·······»·······continue;
»·······»·······»·······grp = g;
»·······»·······»·······ret = 0;
»·······»·······»·······best_ndir = stats.used_dirs;
»·······»·······}

Thanks & Regards,
  Lokesh