[Samba] dfree command cannot report correct disk space

[Jeremy Allison]

On Mon, May 06, 2019 at 03:40:15PM -0400, Manhong Dai via samba wrote:
> Hi,
> 
> my  filesystems is mounted like the below df output, /share is exported in
> samba.
> 
> Filesystem                     Size  Used Avail Use% Mounted on
> /dev/sda1                       50G  9.1G   41G  19% /share
> nfs1:/                          492T  433T   59T  89% /share/group1
> 
> If a 100G file is copied to /share/group1, samba will report the storage
> doesn't have enough space.
> 
> I tried to use 'dfree command' to report a correct disk space, the thing is
> dfree command always gets parameter $1 as '.', and its pwd is always
> '/share'. I have no way to know which directory the user is trying to copy
> to.

Yes, due to the symlink race issue we cd to the share directory
before invoking the script. $cwd will be accurate though.

> By the way, my Samba version is 4.10.2. /share/group1 is mounted as autofs.
> As there are many groups under /share mounted as NFS or other file systems,
> it is awkward to export each group as a samba share.
> 
> How can I fix this? Any input is greatly appreciated!

Problem is you're maintaining a fiction for the clients that
all these mounts are one share. They're not. As the client
thinks it's one single share then the client *knows* that
doing a SMB_FS_SIZE_INFORMATION on the root of the share will
give the total free space on the share.

The clients don't expect that there are different dfree
values below a share - they're simply not coded that
way. The unit of granularity for a dfree is the share,
that's a client assumption, not a server one (the server
passes the path passed in by the client to the dfree
call, it's just that the path is always the share
root).