open FIFOs with O_RDWR should be permitted or rejected

[gwu-ddn]

https://pubs.opengroup.org/onlinepubs/9799919799/functions/open.html#tag_17_372

RATIONALE

Some implementations **permit opening FIFOs with O_RDWR**. Since FIFOs could be implemented in other ways, and since two file descriptors can be used to the same effect, an implementation is allowed to **reject the use of O_RDWR on a FIFO**.

=====
Mostly filesystems will return EACCES from vfs layer (inode_permission ...).

For fuse, if "default_permissions" is turnned off, vfs inode_permission/fuse_permission will by-passed, and fifo_open will be invoked, then return 0 for opening fifo with O_RDWR:

1117 static int fifo_open(struct inode *inode, struct file filp)
...
1198 case FMODE_READ | FMODE_WRITE:
1199 /
1200 * O_RDWR
1201 * POSIX.1 leaves this case "undefined" when O_NONBLOCK is set.
1202 * This implementation will NEVER block on a O_RDWR open, since
1203 * the process can at least talk to itself.
1204 */
1205

pjdfstest/tests/open/06.t:

91 # FIFO.
92
93 expect 0 -u 65534 -g 65534 mkfifo ${n1} 0644
...
106 expect 0 -u 65534 -g 65534 open ${n1} O_RDONLY,O_NONBLOCK
107 expect 'EACCES|ENXIO' -u 65534 -g 65534 open ${n1} O_WRONLY,O_NONBLOCK
108 expect EACCES -u 65534 -g 65534 open ${n1} O_RDWR
109 expect 0 -u 65534 -g 65534 chmod ${n1} 0747
110 expect 0 -u 65533 -g 65534 open ${n1} O_RDONLY,O_NONBLOCK
111 expect 'EACCES|ENXIO' -u 65533 -g 65534 open ${n1} O_WRONLY,O_NONBLOCK
112 expect EACCES -u 65533 -g 65534 open ${n1} O_RDWR

ok 77
not ok 78 - tried '-u 65534 -g 65534 open pjdfstest_329384feb34f4747fd994ebd6104ba81 O_RDWR', expected EACCES, got 0
ok 79
ok 80
ok 81
not ok 82 - tried '-u 65533 -g 65534 open pjdfstest_329384feb34f4747fd994ebd6104ba81 O_RDWR', expected EACCES, got 0
ok 83

The issue is similar as #78.