gdb/testsuite/lib/read1.c

   1 /* This is part of GDB, the GNU debugger.
   2
   3    Copyright 2011-2023 Free Software Foundation, Inc.
   4
   5    This program is free software; you can redistribute it and/or modify
   6    it under the terms of the GNU General Public License as published by
   7    the Free Software Foundation; either version 3 of the License, or
   8    (at your option) any later version.
   9
  10    This program is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13    GNU General Public License for more details.
  14
  15    You should have received a copy of the GNU General Public License
  16    along with this program.  If not, see <http://www.gnu.org/licenses/>.
  17 */
  18
  19 #define _GNU_SOURCE 1
  20 #include <dlfcn.h>
  21 #include <unistd.h>
  22 #include <fcntl.h>
  23 #include <stdlib.h>
  24 #include <string.h>
  25 #include <errno.h>
  26 #include <stdio.h>
  27
  28 /* Default READMORE method.  */
  29 #define READMORE_METHOD_DEFAULT 2
  30
  31 /* Default READMORE sleep time in miliseconds.  */
  32 #define READMORE_SLEEP_DEFAULT 10
  33
  34 /* Helper function.  Intialize *METHOD according to environment variable
  35    READMORE_METHOD, and *SLEEP according to environment variable
  36    READMORE_SLEEP.  */
  37
  38 static void
  39 init_readmore (int *method, unsigned int *sleep, FILE **log)
  40 {
  41   char *env = getenv ("READMORE_METHOD");
  42   if (env == NULL)
  43     *method = READMORE_METHOD_DEFAULT;
  44   else if (strcmp (env, "1") == 0)
  45     *method = 1;
  46   else if (strcmp (env, "2") == 0)
  47     *method = 2;
  48   else
  49     /* Default.  */
  50     *method = READMORE_METHOD_DEFAULT;
  51
  52   env = getenv ("READMORE_SLEEP");
  53   if (env == NULL)
  54     *sleep = READMORE_SLEEP_DEFAULT;
  55   else
  56     *sleep = atoi (env);
  57
  58   env = getenv ("READMORE_LOG");
  59   if (env == NULL)
  60     *log = NULL;
  61   else
  62     *log = fopen (env, "w");
  63 }
  64
  65 /* Wrap 'read', and modify it's behaviour using READ1 or READMORE style.  */
  66
  67 ssize_t
  68 read (int fd, void *buf, size_t count)
  69 {
  70   static ssize_t (*read2) (int fd, void *buf, size_t count) = NULL;
  71   static FILE *log;
  72   int readmore;
  73 #ifdef READMORE
  74   readmore = 1;
  75 #else
  76   readmore = 0;
  77 #endif
  78   static int readmore_method;
  79   static unsigned int readmore_sleep;
  80   if (read2 == NULL)
  81     {
  82       /* Use setenv (v, "", 1) rather than unsetenv (v) to work around
  83          https://core.tcl-lang.org/tcl/tktview?name=67fd4f973a "incorrect
  84          results of 'info exists' when unset env var in one interp and check
  85          for existence from another interp".  */
  86       setenv ("LD_PRELOAD", "", 1);
  87       read2 = dlsym (RTLD_NEXT, "read");
  88       if (readmore)
  89         init_readmore (&readmore_method, &readmore_sleep, &log);
  90     }
  91
  92   /* Only modify 'read' behaviour when reading from the terminal.  */
  93   if (isatty (fd) == 0)
  94     goto fallback;
  95
  96   if (!readmore)
  97     {
  98       /* READ1.  Force read to return only one byte at a time.  */
  99       return read2 (fd, buf, 1);
 100     }
 101
 102   if (readmore_method == 1)
 103     {
 104       /* READMORE, method 1.  Wait a little before doing a read.  */
 105       usleep (readmore_sleep * 1000);
 106       return read2 (fd, buf, count);
 107     }
 108
 109   if (readmore_method == 2)
 110     {
 111       /* READMORE, method 2.  After doing a read, either return or wait
 112          a little and do another read, and so on.  */
 113       ssize_t res, total;
 114       int iteration;
 115       int max_iterations = -1;
 116
 117       total = 0;
 118       for (iteration = 1; ; iteration++)
 119         {
 120           res = read2 (fd, (char *)buf + total, count - total);
 121           if (log != NULL)
 122             fprintf (log,
 123                      "READ (%d): fd: %d, COUNT: %zd, RES: %zd, ERRNO: %s\n",
 124                      iteration, fd, count - total, res,
 125                      res == -1 ? strerror (errno) : "none");
 126           if (res == -1)
 127             {
 128               if (iteration == 1)
 129                 {
 130                   /* Error on first read, report.  */
 131                   total = -1;
 132                   break;
 133                 }
 134
 135               if (total > 0
 136                   && (errno == EAGAIN || errno == EWOULDBLOCK || errno == EIO))
 137                 {
 138                   /* Ignore error, but don't try anymore reading.  */
 139                   errno = 0;
 140                   break;
 141                 }
 142
 143               /* Other error, report back.  */
 144               total = -1;
 145               break;
 146             }
 147
 148           total += res;
 149           if (total == count)
 150             /* Buf full, no need to do any more reading.  */
 151             break;
 152
 153           /* Handle end-of-file.  */
 154           if (res == 0)
 155             break;
 156
 157           if (iteration == max_iterations)
 158             break;
 159
 160           usleep (readmore_sleep * 1000);
 161         }
 162
 163       if (log)
 164         fprintf (log, "READ returning: RES: %zd, ERRNO: %s\n",
 165                  total, total == -1 ? strerror (errno) : "none");
 166       return total;
 167     }
 168
 169  fallback:
 170   /* Fallback, regular read.  */
 171   return read2 (fd, buf, count);
 172 }