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

[Jaegeuk Kim <jaegeuk@kernel.org>]

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.

> 
> >> 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.

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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