pSOSystem System Calls - Read

pREPC+ System Calls fopen
Error Codes
Notes
Refer to Appendix B.
1. The disk files are managed by the pHILE + file system manager and are
designated by pHILE + pathnames (for example, 0.1/abc). The I/O devices are
identified by pSOS+ logical device numbers represented as a string of the form
M.N, where M is the major number and N is the minor number of the I/O device
(for example, 0.1). When reading or writing disk files, the pREPC+ library calls
the pHILE+ file system manager. When reading or writing I/O devices, the
pREPC+ library calls the pSOS+ I/O Supervisor directly.
2. fopen() internally makes a call to the pHILE+ open_f function when it opens
a disk file and the pSOS+ de_open function when it opens an I/O device.
3. If the volume is an NFS volume, two conditions can cause problems related to
the file mode. The conditions are as follows:
a. A file that did not previously exist is created in an NFS volume by the
fopen() call with a UNIX-like privilege mode automatically set to 0x180
(octal 600/rw for the user.) If, for example, the mode in the fopen() call is
manually specified as w, a conflict could result. The pREPC+ library allows
only file operations that are valid for the specified mode. Therefore (using
the preceding example), the pREPC+ library does not allow a read operation
on the following file:
fopen("0.0/file1.dat", "w");
b. The restrictions placed on file operations depend on the mode extended to
files that exist prior to the fopen() call. For example:
fopen("0.0/file2.dat", "r");
succeeds if file2.dat exists prior to the fopen() call. A subsequent read
operation would fail if that file had an access mode (under NFS) that did not
allow a user-read. Currently, no method exists under the pREPC+ library to
change the access mode of an NFS file.
4. Since the underlying mechanism (pHILE+ and pSOS+ I/O device manager) do
not, as of yet, support the concept of text files, pREPC+ treats text files as
binary files. However, for forward compatibility, you must specify the “b”
character in the mode string if the file being opened through fopen contains
pSOSystem System Calls 3-41
3