When I connect an iPod to my Fedora 15 computer and add songs to it using Rhythmbox, the songs are unavailable on the device (the iPod reports "No Music").  I debugged and found that the problem is that ipod-set-info (a libgpod executable) is not running properly.  Details follow.

Here's what's supposed to happen when you connect an iPod:

1. A udev rule defined in /lib/udev/90-libgpod.rules fires and runs /lib/udev/ipod-set-info.
2. ipod-set-info writes a file iPod_Control/Device/SysInfoExtended to the iPod.  This file contains information that libgpod needs in order to properly write files to the iPod.  (See README.SysInfo in the libgpod distribution for more about this.)

On Fedora 15, ipod-set-info fails to write the SysInfoExtended file.  The problem is that Fedora builds libgpod with this configure option (found in libgpod.spec):

  --with-temp-mount-dir=%{_localstatedir}/run/%{name}

That maps to /var/run/libgpod.  Unfortunately that directory does not exist, and ipod-set-info won't create it automatically.  So when ipod-set-info tries to mount the iPod (that happens in mount_ipod() in generic-callout.c), the call "mkdtemp(filename)" fails, and so SysInfoExtended is never written.  And so Rhythmbox can't write songs properly to the iPod.