The iofunc_mount_t mount structure

The mount structure contains information that's common across multiple attributes structures.

Here are the contents of the mount structure (from <sys/iofunc.h>):

typedef struct _iofunc_mount {
  uint32_t       flags;
  uint32_t       conf;
  dev_t          dev;
  int32_t        blocksize;
  iofunc_funcs_t *funcs;
} iofunc_mount_t;

The flags member contains just one flag, IOFUNC_MOUNT_32BIT. This flag indicates that offset in the OCB, and nbytes and inode in the attributes structure, are 32-bit. Note that you can define your own flags in flags, using any of the bits from the constant IOFUNC_MOUNT_FLAGS_PRIVATE.

The conf member contains the following flags:

IOFUNC_PC_CHOWN_RESTRICTED

Indicates if the filesystem is operating in a “chown-restricted” manner, meaning if only root is allowed to chown a file.

IOFUNC_PC_NO_TRUNC

Indicates that the filesystem doesn't truncate the name.

IOFUNC_PC_SYNC_IO

Indicates that the filesystem supports synchronous I/O operations. If this bit isn't set, the following may occur:

• The default iofunc layer _IO_OPEN handler, iofunc_open_default(), fails if the client specifies O_DSYNC, O_RSYNC, or O_SYNC.
• The iofunc_sync_verify() function returns EINVAL.
• Attempts to set O_DSYNC, O_RSYNC, or O_SYNC with fcntl() or the DCMD_ALL_SETFLAGS devctl() command fail.

IOFUNC_PC_LINK_DIR

Indicates that linking/unlinking of directories is allowed.

IOFUNC_PC_ACL

Indicates whether or not the resource manager supports access control lists. For more information about ACLs, see Working with Access Control Lists (ACLs) in the QNX Neutrino Programmer's Guide.

The dev member contains the device number and is described below in “Of device numbers, inodes, and our friend rdev.”

The blocksize describes the native blocksize of the device in bytes. For example, on a typical rotating-medium storage system, this would be the value 512.

Finally, the funcs pointer points to a structure (from <sys/iofunc.h>):

typedef struct _iofunc_funcs {
  unsigned      nfuncs;

  IOFUNC_OCB_T *(*ocb_calloc)
                    (resmgr_context_t *ctp,
                     IOFUNC_ATTR_T *attr);

  void          (*ocb_free)
                    (IOFUNC_OCB_T *ocb);
} iofunc_funcs_t;

As with the connect and I/O functions tables, the nfuncs member should be stuffed with the current size of the table. Use the constant _IOFUNC_NFUNCS for this.

The ocb_calloc and ocb_free function pointers can be filled with addresses of functions to call whenever an OCB is to be allocated or deallocated. We'll discuss why you'd want to use these functions later when we talk about extending OCBs.