[PATCH 3/3] linux: implement ttyname as a wrapper around ttyname_r.
Adhemerval Zanella
adhemerval.zanella@linaro.org
Tue May 4 16:37:27 GMT 2021
On 03/05/2021 22:51, Érico Nogueira via Libc-alpha wrote:
> Big win in binary size and avoids duplicating the logic in multiple
> places.
>
> On x86_64, dropped from 1883206 to 1881790, a 1416 byte decrease.
>
> Also changed logic to track if ttyname_buf has been allocated by
> checking if it's NULL instead of tracking buflen as an additional
> variable.
> ---
>
> I was going to simply change the function to use __fd_to_filename, like
> the 2/3 patch, but this felt like a better improvement. However, I
> haven't studied the implications deeply or verified if the ttyname()
> logic behaved noticeably (or subtly) different than what ttyname_r()
> did.
>
> sysdeps/unix/sysv/linux/ttyname.c | 161 ++----------------------------
> 1 file changed, 9 insertions(+), 152 deletions(-)
>
> diff --git a/sysdeps/unix/sysv/linux/ttyname.c b/sysdeps/unix/sysv/linux/ttyname.c
> index d561ac12f2..a2bb81c78b 100644
> --- a/sysdeps/unix/sysv/linux/ttyname.c
> +++ b/sysdeps/unix/sysv/linux/ttyname.c
> @@ -17,17 +17,9 @@
>
> #include <errno.h>
> #include <limits.h>
> -#include <stddef.h>
> -#include <dirent.h>
> -#include <sys/types.h>
> -#include <sys/stat.h>
> #include <termios.h>
> -#include <unistd.h>
> -#include <string.h>
> #include <stdlib.h>
>
> -#include <_itoa.h>
> -
> #include "ttyname.h"
>
> #if 0
> @@ -35,170 +27,35 @@
> char *__ttyname;
> #endif
Maybe remove this dead code as well.
>
> -static char *getttyname (const char *dev, const struct stat64 *mytty,
> - int save, int *dostat);
> -
> -libc_freeres_ptr (static char *getttyname_name);
> -
> -static char *
> -attribute_compat_text_section
> -getttyname (const char *dev, const struct stat64 *mytty, int save, int *dostat)
> -{
> - static size_t namelen;
> - struct stat64 st;
> - DIR *dirstream;
> - struct dirent64 *d;
> - size_t devlen = strlen (dev) + 1;
> -
> - dirstream = __opendir (dev);
> - if (dirstream == NULL)
> - {
> - *dostat = -1;
> - return NULL;
> - }
> -
> - /* Prepare for the loop. If we already have a buffer copy the directory
> - name we look at into it. */
> - if (devlen < namelen)
> - *((char *) __mempcpy (getttyname_name, dev, devlen - 1)) = '/';
> -
> - while ((d = __readdir64 (dirstream)) != NULL)
> - if ((d->d_fileno == mytty->st_ino || *dostat)
> - && strcmp (d->d_name, "stdin")
> - && strcmp (d->d_name, "stdout")
> - && strcmp (d->d_name, "stderr"))
> - {
> - size_t dlen = _D_ALLOC_NAMLEN (d);
> - if (devlen + dlen > namelen)
> - {
> - free (getttyname_name);
> - namelen = 2 * (devlen + dlen); /* Big enough. */
> - getttyname_name = malloc (namelen);
> - if (! getttyname_name)
> - {
> - *dostat = -1;
> - /* Perhaps it helps to free the directory stream buffer. */
> - (void) __closedir (dirstream);
> - return NULL;
> - }
> - *((char *) __mempcpy (getttyname_name, dev, devlen - 1)) = '/';
> - }
> - memcpy (&getttyname_name[devlen], d->d_name, dlen);
> - if (__stat64 (getttyname_name, &st) == 0
> - && is_mytty (mytty, &st))
> - {
> - (void) __closedir (dirstream);
> -#if 0
> - __ttyname = getttyname_name;
> -#endif
> - __set_errno (save);
> - return getttyname_name;
> - }
> - }
> -
> - (void) __closedir (dirstream);
> - __set_errno (save);
> - return NULL;
> -}
> -
> -
> +#define TTYNAME_BUFLEN (PATH_MAX-1)
> /* Static buffer in `ttyname'. */
> libc_freeres_ptr (static char *ttyname_buf);
Although not really related to this change, since you are touching it
I think it should use a libc_freeres_fn instead:
| static char *ttyname_buf;
|
| libc_freeres_fn (free_mem)
| {
| free (ttyname_buf);
| }
>
> -
> /* Return the pathname of the terminal FD is open on, or NULL on errors.
> The returned storage is good only until the next call to this function. */
> char *
> ttyname (int fd)
> {
> - static size_t buflen;
> - char procname[30];
> - struct stat64 st, st1;
> - int dostat = 0;
> - int doispty = 0;
> - char *name;
> - int save = errno;
> - struct termios term;
> -
> /* isatty check, tcgetattr is used because it sets the correct
> - errno (EBADF resp. ENOTTY) on error. */
> + errno (EBADF resp. ENOTTY) on error. Fast error path to avoid the allocation */
Double space after period and line too long.
> + struct termios term;
> if (__glibc_unlikely (__tcgetattr (fd, &term) < 0))
> return NULL;
>
> - if (__fstat64 (fd, &st) < 0)
> - return NULL;
> -
> - /* We try using the /proc filesystem. */
> - *_fitoa_word (fd, __stpcpy (procname, "/proc/self/fd/"), 10, 0) = '\0';
> -
> - if (buflen == 0)
> + if (ttyname_buf == NULL)
> {
> - buflen = 4095;
> - ttyname_buf = (char *) malloc (buflen + 1);
> + ttyname_buf = malloc (TTYNAME_BUFLEN + 1);
> if (ttyname_buf == NULL)
> {
> - buflen = 0;
> return NULL;
> }
> }
>
Ok.
> - ssize_t len = __readlink (procname, ttyname_buf, buflen);
> - if (__glibc_likely (len != -1))
> - {
> - if ((size_t) len >= buflen)
> - return NULL;
> -
> -#define UNREACHABLE_LEN strlen ("(unreachable)")
> - if (len > UNREACHABLE_LEN
> - && memcmp (ttyname_buf, "(unreachable)", UNREACHABLE_LEN) == 0)
> - {
> - memmove (ttyname_buf, ttyname_buf + UNREACHABLE_LEN,
> - len - UNREACHABLE_LEN);
> - len -= UNREACHABLE_LEN;
> - }
> -
> - /* readlink need not terminate the string. */
> - ttyname_buf[len] = '\0';
> -
> - /* Verify readlink result, fall back on iterating through devices. */
> - if (ttyname_buf[0] == '/'
> - && __stat64 (ttyname_buf, &st1) == 0
> - && is_mytty (&st, &st1))
> - return ttyname_buf;
> -
> - doispty = 1;
> - }
> -
> - if (__stat64 ("/dev/pts", &st1) == 0 && S_ISDIR (st1.st_mode))
> - {
> - name = getttyname ("/dev/pts", &st, save, &dostat);
> - }
> - else
> - {
> - __set_errno (save);
> - name = NULL;
> - }
> -
> - if (!name && dostat != -1)
> + int result = ttyname_r (fd, ttyname_buf, TTYNAME_BUFLEN);
> + if (result != 0)
Why do you need to pass the allocated buffer size minus 1? The ttyname_r
should handle it, it already pass buflen - 1 on readlink for instance.
> {
> - name = getttyname ("/dev", &st, save, &dostat);
> - }
> -
> - if (!name && dostat != -1)
> - {
> - dostat = 1;
> - name = getttyname ("/dev", &st, save, &dostat);
> - }
> -
> - if (!name && doispty && is_pty (&st))
> - {
> - /* We failed to figure out the TTY's name, but we can at least
> - signal that we did verify that it really is a PTY slave.
> - This happens when we have inherited the file descriptor from
> - a different mount namespace. */
> - __set_errno (ENODEV);
> + __set_errno (result);
> return NULL;
> }
> -
> - return name;
> + return ttyname_buf;
> }
>
With this change ttyname now returns ERANGE instead of ENAMETOOLONG if
readlink returns a link larger than the specified buffer, but I think
it should be ok.
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