DJB only sets errno_intr here in error.c int error_intr = #ifdef EINTR EINTR; #else -1; #endif The (errno = error_intr) happens in this block:

DJB only sets errno_intr here in error.c int error_intr = #ifdef EINTR EINTR; #else -1; #endif The (errno = error_intr) happens in this block: default: for (;;) { r = read(fdfile,inbuf,sizeof inbuf); if (r == -1) { if (errno = error_intr) continue; _exit(23); } if (r == 0) break; if (!fetch_ascii) substdio_put(&ss,inbuf,r); else for (i = 0;i < r;++i) { if (inbuf[i] == '\n') substdio_put(&ss,"\r",1); substdio_put(&ss,inbuf + i,1); } } break; Like a lot of DJB code, it's hard to tell exactly what he's trying to do. He could be trying to deal with some weird platform. Where EINTR is defined to something other than 0 that code will cause the read() to be repeated whenever it returns -1 and when the code eventually gets back to the caller errno will be left set to EINTR. But on platforms where EINTR is 0, a read error will exit.