Re: [fuse-devel] fuse: reading device: Unknown error 512

[Miklos S. <mi...@sz...>]

> Please let me know if that is not the right place for this type of
> questions.
> 
> I am seeing this message in the log file of our virtual file system and was
> trying to track its root cause. Inspecting fuse-2.7.2/lib/fuse_kern_chan.c
> shows that this message is printed from fuse_kern_chan_receive() after
> verifying that errno after read() return -1 is not in the set (ENOENT,
> ENODEV, EINTR, EAGAIN). However, per the read() manual pages, read() would
> not set errno to 512, which is strange. And 512 is not a valid errno value.
> My user-space read() implementation appears below and fi->fh was previously
> initialized by opening a temporary file created on the fly on the local
> filesystem (ext3) when calling my open() callback.
> 
>         static int read(const char *path, char *buf, size_t size, off_t
> offset, struct fuse_file_info *fi)
>         {
>             int res;
>             (void) path;
>             res = pread(fi->fh, buf, size, offset);
>             if (res == -1)
>                 res = -errno;
>             return res;
>         }
> Would anyone have a suggestion, please?

This is strange indeed.  512 means ERESTARTSYS, which is a kernel
internal errno value.  But it should never be seen in userspace.

> cat /proc/version
> Linux version 2.6.18-53.1.13.el5xen (moc...@bu...) (gcc
> version 4.1.2 20070626 (Red Hat 4.1.2-14)) #1 SMP Tue Feb 12 13:33:07 EST
> 2008

It doesn't look like a fuse problem (fuse is correctly rejecting the
errno as invalid).  Perhaps it is xen related?

Miklos