Open System Services System Calls Reference Manual (G06.25+, H06.03+)

System Functions (a - d) creat(2)
Opening Guardian Files
If the file is a Guardian file (that is, a file in the /G file system), these rules apply:
• The file can be opened only if it is one of these:
— An odd, unstructured Enscribe file. In this case, it is opened as a regular file with
a primary and secondary extent size that is a multiple of 2. If the extent size is
odd, the open fails.
If the unstructured buffer size was not 4096, a successful open makes the buffer
size 4096 (as if the Guardian procedure SETMODE was called for mode 93 with
a parameter value of 4096).
— An EDIT file (file code 101). In this case, it is opened as a regular file for read-
only access.
— A tty simulation process.
An attempt to open any file (or device) of any other type fails, and errno is set to the
value of [EINVAL]. An attempt to open a volume, subvolume, or process (/G/vol,
/G/vol/subvol,or/G/process, respectively) fails, and errno is set to the value of [EIS-
DIR].
• An attempt to open a subvolume with a reserved name beginning with "ZYQ" (for exam-
ple, /G/vol2/zyq00004) fails, and errno is set to the value of [EACCES].
• An attempt to open a file within a subvolume with a reserved name beginning with
"ZYQ" (for example, /G/vol2/zyq00004/z000002x) fails, and errno is set to the value of
[EACCES].
• If the file is not an EDIT file (that is, the file code is not 101), it is opened in shared
exclusion mode.
• If the file is an EDIT file and read-only access is specified, the file is opened in protected
exclusion mode in the Guardian environment.
• If the file is an EDIT file and write access is specified, the call fails, and errno is set to
the value [EINVAL].
• The maximum number of opens is reported by the sysconf() function as the upper limit
of opens per process. The actual limit depends on other factors, such as the size of the
process file segment (PFS) and the number of existing opens on directories or on files in
the Guardian environment.
• If the open causes file creation, odd unstructured and file code 180 attributes are
assumed.
• If the open causes file creation, the file is given access permissions compatible with the
standard security permissions for the Guardian creator access ID (CAID) of the calling
process.
During creat() function processing, all access permissions are checked. This includes Guardian
environment checks by Guardian standard security mechanisms (and by the Safeguard product)
for Guardian disk file and process access.
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