> :> The are dozens of libc routines which call malloc internally and > return > :> allocated storage. strdup(), opendir(), fopen(), setvbuf(), > asprintf(), > :> and so forth. Dozens. And while we might check some of these for > NULL, > :> we don't check them all, and the ones we do check we tend to conclude > :> a failure other then a memory failure. We would assume that the > directory > :> or file does not exist, for example. How many programmers check errno > :> after such a failure? Very few. How many programmers bother to even > :> *clear* errno before making these calls (since some system calls do not > : ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ > :We're not supposed to have to clear errno unless we have to explicitly > :test if it has changed. We're not supposed to clear it before any system > :call which could possibly fail and set errno. > : > :> set errno if it already non-zero). Virtually nobody. > : ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ > :Erm... WTF?!?! If so, why the HELL are we doing that?!? > > No, wait, I got that wrong I think. > > Oh yah, I remember now. Hmm. How odd. I came across a case where > read() could return -1 and not set errno properly if errno > was already set, but a perusal of the kernel code seems to indicate > that this can't happen. Very weird. >
I thought I saw this somewhere too, but I thought it was more of a case that it was somewhere *inside* read that errno had to be preserved. i.e. errno gets set somewhere at the top of the code, and if it was already set at a certain point, failure was expected, and to pass along the original errno, not the new one. Or perhaps we're sharing a hallucination. :) Kevin To Unsubscribe: send mail to majord...@freebsd.org with "unsubscribe freebsd-hackers" in the body of the message
