0 bytes sized file can't be written to a HAMMER partition

[Antonio Huete Jimenez]

It looks like the code should be changed to:

if (uio->uio_offset < 0 || uio->uio_offset + uio->uio_resid < 0) {
       hammer_done_transaction(&trans);
       return (EFBIG);
}
Applying that change the issue I'm able to copy zero-bytes sized files 
to a HAMMER partition:

master# touch /tmp/qq && cp /tmp/qq /datapool/
master# ls -l /datapool/qq
-rw-r--r--  1 root  wheel  0 Jun 10 19:43 /datapool/qq
master# mount |grep datapool
datapool on /datapool (hammer, local)
Thank you
Antonio Huete

basically the second check was <= instead of < which caught my eye.
I could be wrong, because I haven't dug into the code, but that's the most obvious point in the return (EFBIG) case.
Try that, Antonio, and once youve got a built kernel, try copying a zero-byte file to a HAMMER fs.
Regards.
Jon
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