I decided to give a new try to Calibre a few months ago after buying several O'reilly ebooks. Mainly because my workflow to synchronize my e-reader was to use rsync and I didn't have any easy way to merge several formats of the same ebook nor tracking their reading state.

Luckily one of the features of Calibre is to auto-mount plugged e-readers saving you a manual mount. The sad part was that nothing happened when I plugged my Sony PRS-T2 even though the two were supposed to be compatible.

strace to the rescue! After digging into I/O-related system calls I found that Calibre was parsing /sys/devices directory and doing some things with other sysfs folders to find compatible devices. Oddly my laptop didn't populate the correct folders when I plugged my device. After losing several hours on this issue, someone pointed me to the sysfs layout configuration in the kernel. After checking my configuration I found that CONFIG_SYSFS_DEPRECATED and CONFIG_SYSFS_DEPRECATED_V2 were enabled. These options instruct the kernel to use the sysfs layout used decades ago instead of the new one. After disabling these two options Calibre started to automount the plugged e-reader.

To be honest you should not be affected by this issue since these options are disabled by default since at least 2006.