In "Like the Sun," is the headmaster pleased or angry that Sekhar has told him the truth about his music?

The headmaster is irritated by the truth Sekhar tells him, because the music he asked about was a replacement for something missing in his life. After Sekhar tells him he doesn't like his music, the headmaster gives it up.
When the headmaster calls Sekhar after their discussion, he's clearly annoyed even though his words are positive. He says:

"Your suggestion was useful. I have paid off the music master. No one would tell me the truth about my music all these days. Why such antics at my age! Thank you. By the way, what about those test papers?"

The headmaster loses something he values when he takes Sekhar's opinion to heart. When he was discussing his love of music and lessons with Sekhar, he said that God hadn't given him children but was merciful enough to give him music. It was a replacement for something he wanted deeply and now he's lost that too.
His annoyance is made even more clear when he asks about the test papers. He wants Sekhar to take care of 100 papers and before their discussion about music, he gives Sekhar ten days to complete them. When he calls that night, he insists Sekhar finish all 100 that night. However, Sekhar thinks to himself that sitting up all night grading is a small price to pay for the luxury of the truth.

I would argue that the headmaster is simultaneously pleased and irritated that Sekhar has told him the truth.
First, the headmaster is pleased because he no longer needs to spend money on something he apparently has no talent for. However, he is also a little irritated that he has failed to impress a subordinate with what he believed was his superior musical aptitude. Additionally, up until now, he has "spent a fortune" to pursue his music studies, and he can never recuperate those costs. In immersing himself in his music venture, the headmaster has also invested much emotional capital towards his success.
When Sekhar apprises him of the truth, the headmaster's hopes for future fame and recognition are dashed. The evidence for his irritation rests in his final insistence that Sekhar should turn in the corrected papers the next day; this is contrary to his previous stipulation that his subordinate could have ten days to complete the task.