static int
lock_if_free (lock_info_type *clasher, register char *lfname)
{
while (lock_file_1 (lfname, 0) == 0)
{
int locker;
if (errno != EEXIST)
return -1;
locker = current_lock_owner (clasher, lfname);
if (locker == 2)
{
FREE_LOCK_INFO (*clasher);
return 0; /* We ourselves locked it. */
}
else if (locker == 1)
return 1; /* Someone else has it. */
else if (locker == -1)
return -1; /* current_lock_owner returned strange error. */
/* We deleted a stale lock; try again to lock the file. */
}
return 0;
}
void
lock_file (Lisp_Object fn)
{
register Lisp_Object attack, orig_fn, encoded_fn;
register char *lfname, *locker;
lock_info_type lock_info;
struct gcpro gcpro1;
/* Don't do locking while dumping Emacs.
Uncompressing wtmp files uses call-process, which does not work
in an uninitialized Emacs. */
if (! NILP (Vpurify_flag))
return;
orig_fn = fn;
GCPRO1 (fn);
fn = Fexpand_file_name (fn, Qnil);
encoded_fn = ENCODE_FILE (fn);
/* Create the name of the lock-file for file fn */
MAKE_LOCK_NAME (lfname, encoded_fn);
/* See if this file is visited and has changed on disk since it was
visited. */
{
register Lisp_Object subject_buf;
subject_buf = get_truename_buffer (orig_fn);
if (!NILP (subject_buf)
&& NILP (Fverify_visited_file_modtime (subject_buf))
&& !NILP (Ffile_exists_p (fn)))
call1 (intern ("ask-user-about-supersession-threat"), fn);
}
UNGCPRO;
/* Try to lock the lock. */
if (lock_if_free (&lock_info, lfname) <= 0)
/* Return now if we have locked it, or if lock creation failed */
return;
/* Else consider breaking the lock */
locker = (char *) alloca (strlen (lock_info.user) + strlen (lock_info.host)
+ LOCK_PID_MAX + 9);
sprintf (locker, "%s@%s (pid %lu)", lock_info.user, lock_info.host,
lock_info.pid);
FREE_LOCK_INFO (lock_info);
attack = call2 (intern ("ask-user-about-lock"), fn, build_string (locker));
if (!NILP (attack))
/* User says take the lock */
{
lock_file_1 (lfname, 1);
return;
}
/* User says ignore the lock */
}
static int
current_lock_owner (lock_info_type *owner, char *lfname)
{
int ret;
ptrdiff_t len;
lock_info_type local_owner;
intmax_t n;
char *at, *dot, *colon;
char readlink_buf[READLINK_BUFSIZE];
char *lfinfo = emacs_readlink (lfname, readlink_buf);
/* If nonexistent lock file, all is well; otherwise, got strange error. */
if (!lfinfo)
return errno == ENOENT ? 0 : -1;
/* Even if the caller doesn't want the owner info, we still have to
read it to determine return value. */
if (!owner)
owner = &local_owner;
/* Parse [email protected]:BOOT_TIME. If can't parse, return -1. */
/* The USER is everything before the last @. */
at = strrchr (lfinfo, '@');
dot = strrchr (lfinfo, '.');
if (!at || !dot)
{
if (lfinfo != readlink_buf)
xfree (lfinfo);
return -1;
}
len = at - lfinfo;
owner->user = xmalloc (len + 1);
memcpy (owner->user, lfinfo, len);
owner->user[len] = 0;
/* The PID is everything from the last `.' to the `:'. */
errno = 0;
n = strtoimax (dot + 1, NULL, 10);
owner->pid =
((0 <= n && n <= TYPE_MAXIMUM (pid_t)
&& (TYPE_MAXIMUM (pid_t) < INTMAX_MAX || errno != ERANGE))
? n : 0);
colon = strchr (dot + 1, ':');
/* After the `:', if there is one, comes the boot time. */
n = 0;
if (colon)
{
errno = 0;
n = strtoimax (colon + 1, NULL, 10);
}
owner->boot_time =
((0 <= n && n <= TYPE_MAXIMUM (time_t)
&& (TYPE_MAXIMUM (time_t) < INTMAX_MAX || errno != ERANGE))
? n : 0);
/* The host is everything in between. */
len = dot - at - 1;
owner->host = xmalloc (len + 1);
memcpy (owner->host, at + 1, len);
owner->host[len] = 0;
/* We're done looking at the link info. */
if (lfinfo != readlink_buf)
xfree (lfinfo);
/* On current host? */
if (STRINGP (Fsystem_name ())
&& strcmp (owner->host, SSDATA (Fsystem_name ())) == 0)
{
if (owner->pid == getpid ())
ret = 2; /* We own it. */
else if (owner->pid > 0
&& (kill (owner->pid, 0) >= 0 || errno == EPERM)
&& (owner->boot_time == 0
|| within_one_second (owner->boot_time, get_boot_time ())))
ret = 1; /* An existing process on this machine owns it. */
/* The owner process is dead or has a strange pid (<=0), so try to
zap the lockfile. */
else if (unlink (lfname) < 0)
ret = -1;
else
ret = 0;
}
else
{ /* If we wanted to support the check for stale locks on remote machines,
here's where we'd do it. */
ret = 1;
}
/* Avoid garbage. */
if (owner == &local_owner || ret <= 0)
{
FREE_LOCK_INFO (*owner);
}
return ret;
}
static int
current_lock_owner (lock_info_type *owner, char *lfname)
{
int len, ret;
int local_owner = 0;
char *at, *dot, *colon;
char *lfinfo = 0;
int bufsize = 50;
/* Read arbitrarily-long contents of symlink. Similar code in
file-symlink-p in fileio.c. */
do
{
bufsize *= 2;
lfinfo = (char *) xrealloc (lfinfo, bufsize);
errno = 0;
len = readlink (lfname, lfinfo, bufsize);
#ifdef ERANGE
/* HP-UX reports ERANGE if the buffer is too small. */
if (len == -1 && errno == ERANGE)
len = bufsize;
#endif
}
while (len >= bufsize);
/* If nonexistent lock file, all is well; otherwise, got strange error. */
if (len == -1)
{
xfree (lfinfo);
return errno == ENOENT ? 0 : -1;
}
/* Link info exists, so `len' is its length. Null terminate. */
lfinfo[len] = 0;
/* Even if the caller doesn't want the owner info, we still have to
read it to determine return value, so allocate it. */
if (!owner)
{
owner = (lock_info_type *) alloca (sizeof (lock_info_type));
local_owner = 1;
}
/* Parse [email protected]:BOOT_TIME. If can't parse, return -1. */
/* The USER is everything before the last @. */
at = strrchr (lfinfo, '@');
dot = strrchr (lfinfo, '.');
if (!at || !dot)
{
xfree (lfinfo);
return -1;
}
len = at - lfinfo;
owner->user = (char *) xmalloc (len + 1);
strncpy (owner->user, lfinfo, len);
owner->user[len] = 0;
/* The PID is everything from the last `.' to the `:'. */
owner->pid = atoi (dot + 1);
colon = dot;
while (*colon && *colon != ':')
colon++;
/* After the `:', if there is one, comes the boot time. */
if (*colon == ':')
owner->boot_time = atoi (colon + 1);
else
owner->boot_time = 0;
/* The host is everything in between. */
len = dot - at - 1;
owner->host = (char *) xmalloc (len + 1);
strncpy (owner->host, at + 1, len);
owner->host[len] = 0;
/* We're done looking at the link info. */
xfree (lfinfo);
/* On current host? */
if (STRINGP (Fsystem_name ())
&& strcmp (owner->host, SSDATA (Fsystem_name ())) == 0)
{
if (owner->pid == getpid ())
ret = 2; /* We own it. */
else if (owner->pid > 0
&& (kill (owner->pid, 0) >= 0 || errno == EPERM)
&& (owner->boot_time == 0
|| within_one_second (owner->boot_time, get_boot_time ())))
ret = 1; /* An existing process on this machine owns it. */
/* The owner process is dead or has a strange pid (<=0), so try to
zap the lockfile. */
else if (unlink (lfname) < 0)
ret = -1;
else
ret = 0;
}
else
{ /* If we wanted to support the check for stale locks on remote machines,
here's where we'd do it. */
ret = 1;
}
/* Avoid garbage. */
if (local_owner || ret <= 0)
{
FREE_LOCK_INFO (*owner);
}
return ret;
}
