Re: [f2fs-dev] Questions about using f2fs to format the root partition during Slint installation.

[Didier Spaier <didier@slint.fr>]

Hi,

Le 31/08/2020 à 19:42, Jaegeuk Kim a écrit :
> Hi,
> 
> On 08/23, Didier Spaier wrote:
>> Hi,
>>
>> thanks for your answer, which leads to more questions and a request.
>>
>> I will quote only the relevant parts of this answer below.
>>
>> Le 25/06/2020 à 02:35, Jaegeuk Kim a écrit :
>>> On 06/25, Didier Spaier wrote:
>>
>>>> this email is a follow-up of:
>>>> https://www.mail-archive.com/linux-f2fs-devel@lists.sourceforge.net/msg14390.html
>>
>> ...
>>
>>>> Q1: Comments about this choice of target devices for f2fs, knowing that
>>>> I favor security over performances and that the "auto" option of the
>>>> installer is intended for your grand-mother? I am a grand father myself
>>>> <smile>.
>>>
>>> Which security and performance feature do you want to use in the system?
>>> For example, mkfs.f2fs requires some options like:
>>> - fscrypt : -O encrypt
>>> - quota : -O quota
>>> - fsverity : -O verity
>>> - compression : -O compression -O extra_attr
>>> - casefolding : -O casefold -C utf8
>> Do I understand well that these features are defined in f2fs.h?
>> In Linux 5.4.60:
>> #define F2FS_FEATURE_ENCRYPT		0x0001
>> #define F2FS_FEATURE_BLKZONED		0x0002
>> #define F2FS_FEATURE_ATOMIC_WRITE	0x0004
>> #define F2FS_FEATURE_EXTRA_ATTR		0x0008
>> #define F2FS_FEATURE_PRJQUOTA		0x0010
>> #define F2FS_FEATURE_INODE_CHKSUM	0x0020
>> #define F2FS_FEATURE_FLEXIBLE_INLINE_XATTR	0x0040
>> #define F2FS_FEATURE_QUOTA_INO		0x0080
>> #define F2FS_FEATURE_INODE_CRTIME	0x0100
>> #define F2FS_FEATURE_LOST_FOUND		0x0200
>> #define F2FS_FEATURE_VERITY		0x0400
>> #define F2FS_FEATURE_SB_CHKSUM		0x0800
>> #define F2FS_FEATURE_CASEFOLD		0x1000
>>   
>> I ask because I don't see them listed in a man page where I would have
>> expected to find them, like mkfs.f2fs (8) or mount (8)
>>
>> I don't see them listed in:
>> https://github.com/torvalds/linux/blob/master/Documentation/filesystems/f2fs.rst
>>
>> ... 
> 
> Sorry for inconvenience. Let me enhance documentation a bit.

Thanks in advance. I know that it takes time to update documentation
and that you are busy enough already. 

>>>> Q3. What would be the safest options to include in the relevant line of
>>>> /etc/fstab forthe root partition using f2fs?
>>>
>>> default + any features that you're interested in?
>>> We've been using the below option for several years in Android.
>>> https://android.googlesource.com/device/google/coral/+/refs/heads/master/fstab.hardware#11
>>
>> The mount flags and options are described in f2fs.rst but I don't expect a
>> casual user to read that.
>>
>> So I suggest that all the mount options specific to f2fs be listed in an
>> document intended for end users (man f2fs?) as that could help favor its
>> adoption by Linux distributions as an alternative to ext4 when relevant.
>>
>> Maybe you could consult with util-linux devs, as man mount is part of the
>> util-linux package; to just add a line to the text quoted below?
>>
>> FILESYSTEM-SPECIFIC MOUNT OPTIONS
>>        This section lists options that are specific to particular
>>        filesystems.  Where  possible, you  should  first  consult
>>        filesystem-specific manual pages for details.  Some of those pages
>>        are listed in the following table.
>>               
>>        Filesystem(s)      Manual page
>>        btrfs              btrfs(5)
>>        cifs               mount.cifs(8)
>>        ext2, ext3, ext4   ext4(5)
>>        fuse               fuse(8)
>>        nfs                nfs(5)
>>        tmpfs              tmpfs(5)
>>        xfs                xfs(5)
>>
>> the added line would just be for instance:
>>
>>        f2fs               f2fs(8)
> 
> It seems recent "man mount(8)" moves to guide Documentation/filesystems as well.
> But, I think I need to prepare a sort of "man f2fs(5)" in f2fs-tools.

I'd be glad for that, should be very useful.

> FILESYSTEM-SPECIFIC MOUNT OPTIONS
>        You should consult the respective man page for the filesystem first.  If you want to know what options  the  ext4
>        filesystem  supports, then check the ext4(5) man page.  If that doesn't exist, you can also check the correspond‐
>        ing mount page like mount.cifs(8).  Note that you might have to install the respective userland tools.
> 
>        The following options apply only to certain filesystems.  We sort them by filesystem.  They  all  follow  the  -o
>        flag.
> 
>        What options are supported depends a bit on the running kernel.  More info may be found in the kernel source sub‐
>        directory Documentation/filesystems.
> 
>>
>> Indeed 
>>
>> I know I should propose to contribute writing man f2fs, unfortunately my
>> knowledge of f2fs is very close to non existent.
>>
>> Incidentally, the options listed in
>> https://android.googlesource.com/device/google/coral/+/refs/heads/master/fstab.hardware#11
>> indicate that f2fs is only used for the partition mounted as /data.
>>
>> I don't know Android at all but thought that /system is more or less the
>> equivalent of root (/) in other Linux distributions. If that's the case,
>> why not us also f2fs for it? Maybe I am fully wrong, please correct me.
>> I would be grateful for any pointer to a document explaining the purposes
>> of the various mount points in Android as they differ from the FHS:
>> https://refspecs.linuxfoundation.org/fhs.shtml
> 
> Android /system is a read-only partition which provides a device boot-up, while
> all the data for applications and users are stored in /data as read-write.
> For now, there's no strong motivation to replace the filesystem for /system. :)
> 
>>
>> Best regards,
>>
>> Didier



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