wget: explain clearerr more clearly

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

diff --git a/networking/wget.c b/networking/wget.c
index 48688640a07f72fa22d8bb0c1f56e8a323d2dc75..673113bfc616fe0375a37cd4733543af8477f6b9 100644 (file)
--- a/networking/wget.c
+++ b/networking/wget.c
@@ -466,6 +466,14 @@ static void NOINLINE retrieve_file_data(FILE *dfp, int output_fd)
 
        polldata.fd = fileno(dfp);
        polldata.events = POLLIN | POLLPRI;
+
+       /* Must use nonblocking I/O, otherwise fread will loop
+        * and *block* until it reads full buffer,
+        * which messes up progress bar and/or timing out.
+        * Because of nonblocking I/O, we need to dance
+        * very carefully around EAGAIN. See explanation at
+        * clearerr() call.
+        */
        ndelay_on(polldata.fd);
 #endif
        progress_meter(PROGRESS_START);
@@ -504,7 +512,7 @@ static void NOINLINE retrieve_file_data(FILE *dfp, int output_fd)
                                /* Needed for "stalled" indicator */
                                progress_meter(PROGRESS_BUMP);
                        }
-#endif
+
                        /* fread internally uses read loop, which in our case
                         * is usually exited when we get EAGAIN.
                         * In this case, libc sets error marker on the stream.
@@ -515,6 +523,7 @@ static void NOINLINE retrieve_file_data(FILE *dfp, int output_fd)
                         */
                        clearerr(dfp);
                        errno = 0;
+#endif
                        n = fread(G.wget_buf, 1, rdsz, dfp);
                        /* man fread:
                         * If error occurs, or EOF is reached, the return value