Re: ELOOP from getdents

[Nikolaus Rath <Nikolaus@rath.org>]

Hi,

Really no one any idea about this? 

Adding fsdevel- to Cc, maybe someone there can help..

Best,
Nikolaus'

On Jul 05 2016, Nikolaus Rath <Nikolaus-BTH8mxji4b0@public.gmane.org> wrote:
> Hello,
>
> I'm having trouble exporting a FUSE file system over nfs4
> (cf. https://bitbucket.org/nikratio/s3ql/issues/221/). If there are only
> a few entries in exported directory, `ls` on the NFS mountpoint fails
> with:
>
> # ls -li /mnt/nfs/
> /bin/ls: reading directory /mnt/nfs/: Too many levels of symbolic links
> total 1
> 3 drwx------ 1 root root 0 Jul  5 11:07 lost+found/
> 3 drwx------ 1 root root 0 Jul  5 11:07 lost+found/
> 4 -rw-r--r-- 1 root root 4 Jul  5 11:07 testfile
> 4 -rw-r--r-- 1 root root 4 Jul  5 11:07 testfile
>
> Running strace shows that the getdents() syscall fails with ELOOP:
>
> stat("/mnt/nfs", {st_mode=S_IFDIR|0755, st_size=0, ...}) = 0
> openat(AT_FDCWD, "/mnt/nfs", O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC) = 3
> getdents(3, /* 4 entries */, 32768)     = 112
> getdents(3, /* 2 entries */, 32768)     = 64
> getdents(3, 0xf15c90, 32768)            = -1 ELOOP (Too many levels of symbolic links)
> open("/usr/share/locale/locale.alias", O_RDONLY|O_CLOEXEC) = 4
>
> This happens only when using NFSv4, when mounting with vers=3 the error
> does not occur.
>
> The FUSE file system receives the same requests and responds in the same
> way in both cases:
>
> 2016-07-05 12:22:31.477 21519:fuse-worker-7 s3ql.fs.opendir: started with 1
> 2016-07-05 12:22:31.477 21519:fuse-worker-8 s3ql.fs.readdir: started with 1, 0
> 2016-07-05 12:22:31.478 21519:fuse-worker-8 s3ql.fs.readdir: reporting lost+found with inode 3, generation 0, nlink 1
> 2016-07-05 12:22:31.478 21519:fuse-worker-8 s3ql.fs.readdir: reporting testfile with inode 4, generation 0, nlink 1
> 2016-07-05 12:22:31.479 21519:fuse-worker-9 s3ql.fs.getattr: started with 1
> 2016-07-05 12:22:31.479 21519:fuse-worker-10 s3ql.fs._lookup: started with 1, b'lost+found'
> 2016-07-05 12:22:31.480 21519:fuse-worker-11 s3ql.fs._lookup: started with 1, b'testfile'
> 2016-07-05 12:22:31.481 21519:fuse-worker-12 s3ql.fs.readdir: started with 1, 2
> 2016-07-05 12:22:31.484 21519:fuse-worker-13 s3ql.fs.releasedir: started with 1
>
>
> The numbers refer to inodes. So FUSE first receives an opendir() request
> for inode 1 (the file system root / mountpoint), followed by readdir()
> for the same directory with offset 0. It reports two entries. It then
> receives another readdir for this directory with offset 2, and reports
> that all entries have been returned.
>
> However, for some reason NFSv4 gets confused by this and reports 6
> entries to ls.
>
>
> Can anyone advise what might be happening here?
>
>
> Best,
> -Nikolaus
>
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