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terminal: don't hardcode major number of PTYs

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Hardcoding major numbers sucks. And we generally don't do it, except
when determining whether something is a PTY. Thing though is that we
don't actually need to do that here either, hence don#t.
This commit is contained in:
Lennart Poettering
2021-05-19 17:58:01 +02:00
parent 0ba976e8da
commit 11f3c130aa
2 changed files with 63 additions and 26 deletions
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src/basic/terminal-util.c
+38 -26
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@@ -37,6 +37,7 @@
#include "process-util.h"
#include "socket-util.h"
#include "stat-util.h"
#include "stdio-util.h"
#include "string-util.h"
#include "strv.h"
#include "terminal-util.h"
@@ -962,7 +963,9 @@ int get_ctty_devnr(pid_t pid, dev_t *d) {
}
int get_ctty(pid_t pid, dev_t *ret_devnr, char **ret) {
_cleanup_free_ char *fn = NULL, *b = NULL;
char pty[STRLEN("/dev/pts/") + DECIMAL_STR_MAX(dev_t) + 1];
_cleanup_free_ char *buf = NULL;
const char *fn = NULL, *w;
dev_t devnr;
int r;
@@ -970,44 +973,53 @@ int get_ctty(pid_t pid, dev_t *ret_devnr, char **ret) {
if (r < 0)
return r;
r = device_path_make_canonical(S_IFCHR, devnr, &fn);
r = device_path_make_canonical(S_IFCHR, devnr, &buf);
if (r < 0) {
struct stat st;
if (r != -ENOENT) /* No symlink for this in /dev/char/? */
return r;
if (major(devnr) == 136) {
/* This is an ugly hack: PTY devices are not listed in /dev/char/, as they don't follow the
* Linux device model. This means we have no nice way to match them up against their actual
* device node. Let's hence do the check by the fixed, assigned major number. Normally we try
* to avoid such fixed major/minor matches, but there appears to nother nice way to handle
* this. */
/* Maybe this is PTY? PTY devices are not listed in /dev/char/, as they don't follow the
* Linux device model and hence device_path_make_canonical() doesn't work for them. Let's
* assume this is a PTY for a moment, and check if the device node this would then map to in
* /dev/pts/ matches the one we are looking for. This way we don't have to hardcode the major
* number (which is 136 btw), but we still rely on the fact that PTY numbers map directly to
* the minor number of the pty. */
xsprintf(pty, "/dev/pts/%u", minor(devnr));
if (asprintf(&b, "pts/%u", minor(devnr)) < 0)
return -ENOMEM;
} else {
/* Probably something similar to the ptys which have no symlink in /dev/char/. Let's return
* something vaguely useful. */
if (stat(pty, &st) < 0) {
if (errno != ENOENT)
return -errno;
r = device_path_make_major_minor(S_IFCHR, devnr, &fn);
} else if (S_ISCHR(st.st_mode) && devnr == st.st_rdev) /* Bingo! */
fn = pty;
if (!fn) {
/* Doesn't exist, or not a PTY? Probably something similar to the PTYs which have no
* symlink in /dev/char/. Let's return something vaguely useful. */
r = device_path_make_major_minor(S_IFCHR, devnr, &buf);
if (r < 0)
return r;
fn = buf;
}
}
} else
fn = buf;
if (!b) {
const char *w;
w = path_startswith(fn, "/dev/");
if (!w)
return -EINVAL;
w = path_startswith(fn, "/dev/");
if (w) {
b = strdup(w);
if (!b)
return -ENOMEM;
} else
b = TAKE_PTR(fn);
}
if (ret) {
_cleanup_free_ char *b = NULL;
b = strdup(w);
if (!b)
return -ENOMEM;
if (ret)
*ret = TAKE_PTR(b);
}
if (ret_devnr)
*ret_devnr = devnr;