70 lines
2.2 KiB
C
70 lines
2.2 KiB
C
/*
|
|
* This file is part of Jehanne.
|
|
*
|
|
* Copyright (C) 2016 Giacomo Tesio <giacomo@tesio.it>
|
|
*
|
|
* Jehanne is free software: you can redistribute it and/or modify
|
|
* it under the terms of the GNU General Public License as published by
|
|
* the Free Software Foundation, version 2 of the License.
|
|
*
|
|
* Jehanne is distributed in the hope that it will be useful,
|
|
* but WITHOUT ANY WARRANTY; without even the implied warranty of
|
|
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
|
|
* GNU General Public License for more details.
|
|
*
|
|
* You should have received a copy of the GNU General Public License
|
|
* along with Jehanne. If not, see <http://www.gnu.org/licenses/>.
|
|
*/
|
|
|
|
#include <u.h>
|
|
#include <libc.h>
|
|
|
|
/* ocreate works like the Plan 9 create(2) syscall, but with different races.
|
|
* In Plan 9 there is a race due to the different behaviour between the
|
|
* create syscall and the Tcreate message in 9P2000 when the file already exists:
|
|
* see https://github.com/brho/plan9/blob/master/sys/src/9/port/chan.c#L1564-L1603
|
|
* for details.
|
|
*
|
|
* In Jehanne the create syscall fails on existing files just like the Tcreate message.
|
|
* However the Plan 9/UNIX semantic is often useful, thus ocreate mimic it in userspace.
|
|
* As wisely noted by Charles Forsyth, such implementation introduce a different race
|
|
* due to the multiple evaluations of the path: on concurrent namespace changes, the
|
|
* different syscalls here could be handled by different devices/fileservers.
|
|
* However, given the user is responsible of such namespace changes, we prefer this race
|
|
* to the original Plan 9 one.
|
|
*
|
|
* For more info see http://marc.info/?t=146412533100003&r=1&w=2
|
|
*/
|
|
int
|
|
jehanne_ocreate(const char *path, unsigned int omode, unsigned int perm)
|
|
{
|
|
int fd;
|
|
Dir *s;
|
|
|
|
fd = sys_open(path, omode|OTRUNC);
|
|
if(fd < 0){
|
|
fd = sys_create(path, omode, perm);
|
|
if(fd < 0){
|
|
fd = sys_open(path, omode|OTRUNC);
|
|
if(fd < 0)
|
|
goto Done;
|
|
} else {
|
|
goto Done;
|
|
}
|
|
}
|
|
|
|
s = jehanne_dirfstat(fd);
|
|
if(s == nil){
|
|
sys_close(fd);
|
|
return -1;
|
|
}
|
|
if(s->mode != perm){
|
|
s->mode = perm;
|
|
jehanne_dirfwstat(fd, s); /* we ignore the return value, the device/server is allowed to ignore us */
|
|
}
|
|
jehanne_free(s);
|
|
|
|
Done:
|
|
return fd;
|
|
}
|