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hexdump(1): Speed up -s flag on devices

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Using the -s flag on devices is extraordinarily slow due to using fseek(3) a
little too conservatively. Address this by using fseek on character/block
devices as well, falling back to getchar(3) only if we fail to seek or we're
operating on tape drives, where fseek may succeed while not actually being
supported.

PR:		86485
Submitted by:	arundel (originally; modified since then)
Reviewed by:	cem
Differential Revision:	https://reviews.freebsd.org/D10939
This commit is contained in:
Kyle Evans 2018-01-05 01:46:41 +00:00
parent 09f07b0017
commit df7b0169fa
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=327567
1 changed files with 36 additions and 12 deletions
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48
usr.bin/hexdump/display.c
View file

@ -39,6 +39,8 @@ __FBSDID("$FreeBSD$");
#include <sys/param.h>
#include <sys/capsicum.h>
#include <sys/conf.h>
#include <sys/ioctl.h>
#include <sys/stat.h>
#include <capsicum_helpers.h>
@ -57,6 +59,7 @@ static off_t address; /* address/offset in stream */
static off_t eaddress; /* end address */
static void print(PR *, u_char *);
static void noseek(void);
void
display(void)
@ -386,7 +389,7 @@ next(char **argv)
void
doskip(const char *fname, int statok)
{
int cnt;
int type;
struct stat sb;
if (statok) {
@ -398,16 +401,37 @@ doskip(const char *fname, int statok)
return;
}
}
if (statok && S_ISREG(sb.st_mode)) {
if (fseeko(stdin, skip, SEEK_SET))
err(1, "%s", fname);
address += skip;
skip = 0;
} else {
for (cnt = 0; cnt < skip; ++cnt)
if (getchar() == EOF)
break;
address += cnt;
skip -= cnt;
if (!statok || S_ISFIFO(sb.st_mode) || S_ISSOCK(sb.st_mode)) {
noseek();
return;
}
if (S_ISCHR(sb.st_mode) || S_ISBLK(sb.st_mode)) {
if (ioctl(fileno(stdin), FIODTYPE, &type))
err(1, "%s", fname);
/*
* Most tape drives don't support seeking,
* yet fseek() would succeed.
*/
if (type & D_TAPE) {
noseek();
return;
}
}
if (fseeko(stdin, skip, SEEK_SET)) {
noseek();
return;
}
address += skip;
skip = 0;
}
static void
noseek(void)
{
int count;
for (count = 0; count < skip; ++count)
if (getchar() == EOF)
break;
address += count;
skip -= count;
}