To the best of my knowledge, only two of his novels have been filmed.
"The Guide", made in Hindi and English by the legendary Dev Anand, was a huge commercial success but a complete disaster as an adaptation - RK himself was known to have been unhappy with it. Some of this dissatisfaction may also have had to do with the fact that Dev Anand ended up not paying RK a farthing for the filming rights - a fact mentioned by RK with typical self-deprecatory humor in his autobiography. The film still deserves mention as a milestone in Hindi cinema and for its brilliant music.
The other novel which was made into a film was "Mr. Sampat", by S.S. Vasan of Gemini Films with the inimitable Moti Lal in the lead.
The short stories of "Malgudi Days" were serialized on Indian television a while ago. I however wouldn't walk too far to see them.
My view: any attempt to film Narayan is foolhardy at best.
Sujeet