[Pgubook-readers] .equ O_CREAT_WRONLY_TRUNC, 03101

[Emmet Ford]

In toupper.c in chapter 5, we have:

.equ O_CREAT_WRONLY_TRUNC, 03101

This is preceded by a comment inviting the reader to see 
/usr/include/asm/fcntl.h for other options to the open system call. I 
went and looked at /usr/include/asm/fcntl.h, using the opportunity to OR 
together O_CREAT, O_WRONLY and O_TRUNC. But I did not get 03101. 
Instead, I came up with 01101. The only way I was able to arrive at 
03101 was to OR in O_APPEND on top of O_CREAT, O_WRONLY and O_TRUNC.

I gather that tossing in an extraneous O_APPEND doesn't do any harm, as 
it appears to get trumped by O_TRUNC, but it doesn't seem like a good 
thing to be doing on general principle. One could conceive of an 
implementation of the open system call that takes exception to such a 
combination. Unless, of course, I've totally missed the boat on this one.

I am enjoying this book. It's very interesting that the author has 
managed to put off the obligatory discussion of number systems to 
chapter 10.

--Emmet Ford