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cmp: be more robust if lseek fails

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* src/cmp.c (main, cmp): If lseek fails,
don’t assume the file position is -1.
This commit is contained in:
Paul Eggert 2023-06-21 22:45:56 -07:00
parent ff1096a0c2
commit 69ea279bbb
1 changed files with 34 additions and 18 deletions
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52
src/cmp.c
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@ -320,9 +320,12 @@ main (int argc, char **argv)
if (0 <= stat_buf[0].st_size && 0 <= stat_buf[1].st_size
&& 0 < same_file (&stat_buf[0], &stat_buf[1])
&& same_file_attributes (&stat_buf[0], &stat_buf[1])
&& file_position (0) == file_position (1))
return EXIT_SUCCESS;
&& same_file_attributes (&stat_buf[0], &stat_buf[1]))
{
off_t pos = file_position (0);
if (0 <= pos && pos == file_position (1))
return EXIT_SUCCESS;
}
/* If output is redirected to the null device, we can avoid some of
the work. */
@ -347,14 +350,22 @@ main (int argc, char **argv)
&& 0 < stat_buf[0].st_size && S_ISREG (stat_buf[0].st_mode)
&& 0 < stat_buf[1].st_size && S_ISREG (stat_buf[1].st_mode))
{
off_t s0 = stat_buf[0].st_size - file_position (0);
off_t s1 = stat_buf[1].st_size - file_position (1);
if (s0 < 0)
s0 = 0;
if (s1 < 0)
s1 = 0;
if (s0 != s1 && (bytes < 0 || MIN (s0, s1) < bytes))
exit (EXIT_FAILURE);
off_t pos0 = file_position (0);
if (0 <= pos0)
{
off_t pos1 = file_position (1);
if (0 <= pos1)
{
off_t s0 = stat_buf[0].st_size - pos0;
off_t s1 = stat_buf[1].st_size - pos1;
if (s0 < 0)
s0 = 0;
if (s1 < 0)
s1 = 0;
if (s0 != s1 && (bytes < 0 || MIN (s0, s1) < bytes))
exit (EXIT_FAILURE);
}
}
}
/* Guess a good block size for the files. */
@ -403,11 +414,15 @@ cmp (void)
for (int f = 0; f < 2; f++)
if (0 < stat_buf[f].st_size && S_ISREG (stat_buf[f].st_mode))
{
off_t file_bytes = stat_buf[f].st_size - file_position (f);
if (file_bytes < byte_number_max)
byte_number_max = file_bytes;
}
{
int pos = file_position (f);
if (0 <= pos)
{
off_t file_bytes = stat_buf[f].st_size - pos;
if (file_bytes < byte_number_max)
byte_number_max = file_bytes;
}
}
for (offset_width = 1; (byte_number_max /= 10) != 0; offset_width++)
continue;
@ -416,7 +431,7 @@ cmp (void)
for (int f = 0; f < 2; f++)
{
off_t ig = ignore_initial[f];
if (ig && file_position (f) == -1)
if (ig && file_position (f) < 0)
{
/* lseek failed; read and discard the ignored initial prefix. */
do
@ -699,7 +714,8 @@ sprintc (char *buf, unsigned char c)
}
/* Position file F to ignore_initial[F] bytes from its initial position,
and yield its new position. Don't try more than once. */
and yield its new position. Return a negative value on failure.
Don't try more than once. */
static off_t
file_position (int f)