Giacomo Tesio
713eb8843f
There are a few issues with Plan 9's `access`:
- it has side effects: to test the actual access (that the file
servers can allow or deny according to complex custom rules)
it opens and then closes the file, allocating (and disposing) the fd
- it does not work on directories, since
- they cannot be opened for writing, despite the fact that to
create a file in a directory you must be granted write access on
that directory
- they cannot be opened for execution, despite the fact that to
access a file in a directory you must be granted execution access
on that directory
Despite the fact that `access` (even on UNIX) is a violation of the
"tell, don't ask" principle (the access could be forbidden just after
its successful return, making subsequent `open` fail anyway), this
fact smells of a little design error in the file interface.
So, right now we choose to let the libposix's `access` lie on directories:
it will always return 0 on AWRITE and AEXEC for them, accepting that
a successive create/mkdir may fail.
However, a cleaner file API and protocol should allow a simpler `access`
to be implemented for directories too.
46 lines
1.2 KiB
C
46 lines
1.2 KiB
C
/*
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* This file is part of Jehanne.
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*
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* Copyright (C) 2017 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 <lib9.h>
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void
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main(void)
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{
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char *err = nil;
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if(access("/tmp", AEXIST) != 0)
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err = "/tmp does not exists";
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else if(access("/tmp", AREAD) != 0)
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err = "/tmp is not readable";
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/* NOTE:
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* In Plan 9 access(AWRITE) and access(AEXEC) in directories
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* fail despite the actual permission of the directory.
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*
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else if(access("/tmp", AWRITE) != 0)
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err = "/tmp is not writeable";
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else if(access("/tmp", AEXEC) != 0)
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err = "/tmp is not traversable";
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*/
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if(err == nil){
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print("PASS\n");
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exits("PASS");
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} else {
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print("FAIL: %s\n", err);
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exits("FAIL");
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}
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}
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