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