Re: No space left errors on shutdown with systemd-homed /home dir

[Goffredo Baroncelli <kreijack@inwind.it>]

On 29/01/2022 19.01, Chris Murphy wrote:
> On Sat, Jan 29, 2022 at 2:53 AM Goffredo Baroncelli <kreijack@libero.it> wrote:
>>
>> I think that for the systemd uses cases (singled device FS), a simpler
>> approach would be:
>>
>>       fstatfs(fd, &sfs)
>>       needed = sfs.f_blocks - sfs.f_bavail;
>>       needed *= sfs.f_bsize
>>
>>       needed = roundup_64(needed, 3*(1024*1024*1024))
>>
>> Comparing the original systemd-homed code, I made the following changes
>> - 1) f_bfree is replaced by f_bavail (which seem to be more consistent to the disk usage; to me it seems to consider also the metadata chunk allocation)
>> - 2) the needing value is rounded up of 3GB in order to consider a further 1 data chunk and 2 metadata chunk (DUP))
>>
>> Comments ?
> 
> I'm still wondering if such a significant shrink is even indicated, in
> lieu of trim. Isn't it sufficient to just trim on logout, thus
> returning unused blocks to the underlying filesystem? 

I agree with you. In Fedora 35, and the default is ext4+luks+trim
which provides the same results. However I remember that in the past the default
was btrfs+luks+shrunk. I think that something is changed i.

However, I want to provide do the systemd folks a suggestion ho change the code.
Even a warning like: "it doesn't work that because this, please drop it"
would be sufficient.

> And then do an
> fs resize (shrink or grow) as needed on login, so that the user home
> shows ~80% of the free space in the underlying file system?
> 
> homework-luks.c:3407:                                /* Before we
> shrink, let's trim the file system, so that we need less space on disk
> during the shrinking */
> 
> 
> 


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