linux-ext4 - [Bug 92271] Provide a way to really delete files, please

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Date:	Mon, 02 Feb 2015 11:13:06 +0000
From:	bugzilla-daemon@...zilla.kernel.org
To:	linux-ext4@...r.kernel.org
Subject: [Bug 92271] Provide a way to really delete files, please

https://bugzilla.kernel.org/show_bug.cgi?id=92271

--- Comment #20 from Alexander Holler <holler@...oftware.de> ---
My proof of concepts now works for fat and ext4 (just by overwriting blocks w/o
secure_trim, but that's not necessary for the proof):

=====
laptopahbt ~ # dd if=/dev/zero of=/tmp/test.img bs=1M count=50
50+0 Datensätze ein
50+0 Datensätze aus
52428800 Bytes (52 MB) kopiert, 0,0372579 s, 1,4 GB/s
laptopahbt ~ # mkfs.ext4 /tmp/test.img                 
mke2fs 1.42.10 (18-May-2014)
Blöcke des Gerätes werden verworfen: erledigt                        
Creating filesystem with 51200 1k blocks and 12824 inodes
Filesystem UUID: fece1e42-07d5-449f-be29-650a8514648b
Superblock-Sicherungskopien gespeichert in den Blöcken: 
        8193, 24577, 40961

Platz für Gruppentabellen wird angefordert: erledigt                        
Inode-Tabellen werden geschrieben: erledigt                        
Erstelle Journal (4096 Blöcke): erledigt
Schreibe Superblöcke und Dateisystem-Accountinginformationen: erledigt

laptopahbt ~ # grep -a akrakadabra /tmp/test.img 
laptopahbt ~ # mount -o loop /tmp/test.img /mnt/
laptopahbt ~ # echo akrakadabra >/mnt/foo.txt
laptopahbt ~ # umount /mnt/
laptopahbt ~ # grep -a akrakadabra /tmp/test.img 
�@@#����▒�����7((�▒���((����7((+Q��~ ((s��c7((i���H�((�1akrakadabra
laptopahbt ~ # mount -o loop /tmp/test.img /mnt/
laptopahbt ~ # rm -s /mnt/foo.txt 
laptopahbt ~ # umount /mnt/
laptopahbt ~ # grep -a akrakadabra /tmp/test.img 
laptopahbt ~ # mount -o loop /tmp/test.img /mnt/
laptopahbt ~ # echo akrakadabra >/mnt/foo.txt
laptopahbt ~ # umount /mnt/
laptopahbt ~ # mount -o loop /tmp/test.img /mnt/
laptopahbt ~ # rm /mnt/foo.txt 
laptopahbt ~ # umount /mnt/
laptopahbt ~ # grep -a akrakadabra /tmp/test.img 
�@@#����▒�����7((�▒���((����7((+Q��~ ((s��c7((i���H�((�1akrakadabra
laptopahbt ~ # cd /usr/src/linux
laptopahbt linux # PAGER= git diff --stat HEAD~5
 arch/x86/syscalls/syscall_32.tbl      |  1 +
 arch/x86/syscalls/syscall_64.tbl      |  1 +
 fs/ext4/ext4.h                        |  2 ++
 fs/ext4/mballoc.c                     | 21 ++++++++++++++++++++-
 fs/ext4/super.c                       | 10 ++++++++++
 fs/fat/fat.h                          |  1 +
 fs/fat/fatent.c                       | 17 +++++++++++++++++
 fs/fat/inode.c                        | 14 ++++++++++++++
 fs/namei.c                            | 35 ++++++++++++++++++++++++++++++-----
 include/asm-generic/audit_dir_write.h |  1 +
 include/linux/fs.h                    |  1 +
 include/linux/syscalls.h              |  1 +
 include/uapi/asm-generic/unistd.h     |  4 +++-
 tools/perf/builtin-trace.c            |  2 ++
 14 files changed, 104 insertions(+), 7 deletions(-)
=====

Most changes are to add the new syscall unlinkat_s(), the changes for fat and
ext4 itself are pretty small.

Will post patches when I've found the time to make them such, that I don't end
up again in silly discussions.

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