Identifying write access to mmcblk* from userland?

[meino....@gmx.de]

Hi,

one can set different triggers to blink the user LEDs on the
beaglebone & the LCD7 cape.
Beside others I found mmcblk0 as a trigger -- after activating
this, the LED acts as the LED normally found as HD-LED on desktop PCs.
Is it possible -- without modifyng the kernel source -- to monitor
only the write accesses with the LED?

Thank you very much in advance for any help!
Have a nice weekend!
Best regards,
mcc