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/* This is part of GDB, the GNU debugger.
Copyright 2011-2023 Free Software Foundation, Inc.
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#define _GNU_SOURCE 1
#include <dlfcn.h>
#include <unistd.h>
#include <fcntl.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <stdio.h>
/* Default READMORE method. */
#define READMORE_METHOD_DEFAULT 2
/* Default READMORE sleep time in miliseconds. */
#define READMORE_SLEEP_DEFAULT 10
/* Helper function. Intialize *METHOD according to environment variable
READMORE_METHOD, and *SLEEP according to environment variable
READMORE_SLEEP. */
static void
init_readmore (int *method, unsigned int *sleep, FILE **log)
{
char *env = getenv ("READMORE_METHOD");
if (env == NULL)
*method = READMORE_METHOD_DEFAULT;
else if (strcmp (env, "1") == 0)
*method = 1;
else if (strcmp (env, "2") == 0)
*method = 2;
else
/* Default. */
*method = READMORE_METHOD_DEFAULT;
env = getenv ("READMORE_SLEEP");
if (env == NULL)
*sleep = READMORE_SLEEP_DEFAULT;
else
*sleep = atoi (env);
env = getenv ("READMORE_LOG");
if (env == NULL)
*log = NULL;
else
*log = fopen (env, "w");
}
/* Wrap 'read', and modify it's behaviour using READ1 or READMORE style. */
ssize_t
read (int fd, void *buf, size_t count)
{
static ssize_t (*read2) (int fd, void *buf, size_t count) = NULL;
static FILE *log;
int readmore;
#ifdef READMORE
readmore = 1;
#else
readmore = 0;
#endif
static int readmore_method;
static unsigned int readmore_sleep;
if (read2 == NULL)
{
/* Use setenv (v, "", 1) rather than unsetenv (v) to work around
https://core.tcl-lang.org/tcl/tktview?name=67fd4f973a "incorrect
results of 'info exists' when unset env var in one interp and check
for existence from another interp". */
setenv ("LD_PRELOAD", "", 1);
read2 = dlsym (RTLD_NEXT, "read");
if (readmore)
init_readmore (&readmore_method, &readmore_sleep, &log);
}
/* Only modify 'read' behaviour when reading from the terminal. */
if (isatty (fd) == 0)
goto fallback;
if (!readmore)
{
/* READ1. Force read to return only one byte at a time. */
return read2 (fd, buf, 1);
}
if (readmore_method == 1)
{
/* READMORE, method 1. Wait a little before doing a read. */
usleep (readmore_sleep * 1000);
return read2 (fd, buf, count);
}
if (readmore_method == 2)
{
/* READMORE, method 2. After doing a read, either return or wait
a little and do another read, and so on. */
ssize_t res, total;
int iteration;
int max_iterations = -1;
total = 0;
for (iteration = 1; ; iteration++)
{
res = read2 (fd, (char *)buf + total, count - total);
if (log != NULL)
fprintf (log,
"READ (%d): fd: %d, COUNT: %zd, RES: %zd, ERRNO: %s\n",
iteration, fd, count - total, res,
res == -1 ? strerror (errno) : "none");
if (res == -1)
{
if (iteration == 1)
{
/* Error on first read, report. */
total = -1;
break;
}
if (total > 0
&& (errno == EAGAIN || errno == EWOULDBLOCK || errno == EIO))
{
/* Ignore error, but don't try anymore reading. */
errno = 0;
break;
}
/* Other error, report back. */
total = -1;
break;
}
total += res;
if (total == count)
/* Buf full, no need to do any more reading. */
break;
/* Handle end-of-file. */
if (res == 0)
break;
if (iteration == max_iterations)
break;
usleep (readmore_sleep * 1000);
}
if (log)
fprintf (log, "READ returning: RES: %zd, ERRNO: %s\n",
total, total == -1 ? strerror (errno) : "none");
return total;
}
fallback:
/* Fallback, regular read. */
return read2 (fd, buf, count);
}
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