Additional information.

From: Masato Asou <a...@soum.co.jp>
Subject: Use `if (retval == -1)' instead of 'if (retval < 0)'
Date: Wed, 14 Aug 2019 13:42:13 +0900 (JST)

> Hi tech,
> 
> Use `if (retval == -1)' instead of 'if (retval < 0)' when check the
> return value of system call.
> 
> How about it?
> 
> RCS file: /cvs/src/lib/libedit/readline.c,v
> retrieving revision 1.28
> diff -u -p -u -r1.28 readline.c
> --- readline.c  28 Jun 2019 13:32:42 -0000      1.28
> +++ readline.c  14 Aug 2019 04:38:55 -0000
> @@ -2112,7 +2112,7 @@ _rl_event_read_char(EditLine *el, wchar_
>                 return -1;
>  #endif
>  
> -               if (num_read < 0 && errno == EAGAIN)
> +               if (num_read == -1 && errno == EAGAIN)
>                         continue;
>                 if (num_read == 0)
>                         continue;
> --
> ASOU Masato

The valiable num_read has a return value of READ(2) system call as follows:

   2090         while (rl_event_hook) {
   2091
   2092                 (*rl_event_hook)();
   2093
   2094 #if defined(FIONREAD)
   2095                 if (ioctl(el->el_infd, FIONREAD, &n) == -1)
   2096                         return -1;
   2097                 if (n)
   2098                         num_read = read(el->el_infd, &ch, 1);
   2099                 else
   2100                         num_read = 0;
   2101 #elif defined(F_SETFL) && defined(O_NDELAY)
   2102                 if ((n = fcntl(el->el_infd, F_GETFL)) == -1)
   2103                         return -1;
   2104                 if (fcntl(el->el_infd, F_SETFL, n|O_NDELAY) ==
   -1)
   2105                         return -1;
   2106                 num_read = read(el->el_infd, &ch, 1);
   2107                 if (fcntl(el->el_infd, F_SETFL, n))
   2108                         return -1;
   2109 #else
   2110                 /* not non-blocking, but what you gonna do? */
   2111                 num_read = read(el->el_infd, &ch, 1);
   2112                 return -1;
   2113 #endif
   2114
   2115                 if (num_read < 0 && errno == EAGAIN)
   2116                         continue;
   2117                 if (num_read == 0)
   2118                         continue;
   2119                 break;
   2120         }
--
ASOU Masato

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