Updated: April 19, 2023

I/O attribute structure


#include <sys/iofunc.h>

typedef struct _iofunc_attr {
    IOFUNC_MOUNT_T                  *mount;
    struct _iofunc_mmap_list        *mmap_list;
    struct _iofunc_lock_list        *lock_list;
    void                            *acl;
    union {
        void                        *lockobj;
        pthread_mutex_t             lock;
    uint32_t                        flags;
    uint16_t                        count;
    uint16_t                        rcount;
    uint16_t                        wcount;
    uint16_t                        rlocks;
    uint16_t                        wlocks;
    uint16_t                        reserved;
 #if __OFF_BITS__ == 64
    off_t                           nbytes;
    ino_t                           inode;
    off64_t                         nbytes;
    ino64_t                         inode;
#elif _IOFUNC_OFFSET_BITS - 0 == 32
 #if __OFF_BITS__ == 32
  #if defined(__LITTLEENDIAN__)
    off_t                           nbytes;
    off_t                           nbytes_hi;
    ino_t                           inode;
    ino_t                           inode_hi;
  #elif defined(__BIGENDIAN__)
    off_t                           nbytes_hi;
    off_t                           nbytes;
    ino_t                           inode_hi;
    ino_t                           inode;
   #error endian not configured for system
  #if defined(__LITTLEENDIAN__)
    int32_t                         nbytes;
    int32_t                         nbytes_hi;
    int32_t                         inode;
    int32_t                         inode_hi;
  #elif defined(__BIGENDIAN__)
    int32_t                         nbytes_hi;
    int32_t                         nbytes;
    int32_t                         inode_hi;
    int32_t                         inode;
   #error endian not configured for system
 #error _IOFUNC_OFFSET_BITS value is unsupported
    uid_t                           uid;
    gid_t                           gid;
    time_t                          mtime;
    time_t                          atime;
    time_t                          ctime;
    mode_t                          mode;
    nlink_t                         nlink;
    dev_t                           rdev;
    unsigned                        mtime_ns;
    unsigned                        atime_ns;
    unsigned                        ctime_ns;
} iofunc_attr_t;


The iofunc_attr_t structure describes the data and state associated with a service offered by a resource manager. An attribute structure is often associated with a specific name (e.g., /dev/ser1, /dev/ser2), but need not be (e.g., a pipe created by a call to pipe()). You typically use iofunc_attr_init() to initialize this structure.

The members include the following:

A pointer to a structure with information about the mountpoint. By default, this structure is of type iofunc_mount_t, but you can specify your own structure by changing the IOFUNC_MOUNT_T manifest.
mmap_list and lock_list
To manage their particular functionality on the resource, the mmap_list member is used by iofunc_mmap(), iofunc_mmap_default(), and iofunc_mmap_default_ext(); the lock_list member is used by iofunc_lock_default(). Generally, you shouldn't need to modify or examine these members.
Access control lists.
lockobj and lock
(QNX Neutrino 7.1 or later) Members of a union that provide a way to lock the attribute structure. To support multiple threads in your resource manager, you'll need to lock the attribute structure so that only one thread at a time is allowed to change it. The attribute structure can be locked recursively.
  • The default behavior is to use the lock member, which is a built-in lock mutex. If you use iofunc_attr_init() to initialize the structure, it initializes the built-in lock mutex (lock) using a static lock initializer.

    The resource manager layer automatically locks the attribute structure (using iofunc_attr_lock()) for you when certain handler functions are called (i.e., IO_*). You can lock the attribute structure by calling iofunc_attr_lock() or iofunc_attr_trylock(); unlock it by calling iofunc_attr_unlock().

  • If you want to use an external lock object, override the built-in lock by pointing the lockobj member to the external lock object. You also need to provide your own functions to lock and unlock the attribute structure and set the appropriate members of the funcs structure in the iofunc_mount_t structure.
Flags that your resource manager can set to indicate the state of the resource. This member is a combination of the following flags:
The access time is no longer valid. Typically set on a read from the resource.
The change of status time is no longer valid. Typically set when the information for a file changes.
The access control list has changed.
The mode has changed.
The number of links has changed.
The uid or the gid has changed.
The rdev member has changed, e.g., mknod().
The size has changed.
One or more of mtime, atime, or ctime has changed.
The modification time is no longer valid. Typically set on a write to the resource.
(QNX Neutrino 7.0 or later) The attribute structure includes the fields used for nanosecond-resolution timestamps, mtime_ns, atime_ns, and ctime_ns.

You can use these flags to determine which fields of the attribute structure have been modified by the various iofunc-layer helper routines. That way, if you need to write the entries to some medium, you can write just those that have changed. In addition to the above, your resource manager can use in any way the bits in the range defined by IOFUNC_ATTR_PRIVATE (see <sys/iofunc.h>).

count, rcount, wcount, rlocks and wlocks
Several counters are stored in the attribute structure and are incremented/decremented by some of the iofunc layer helper functions. Both the functionality and the actual contents of the message received from the client determine which specific members are affected.
This counter: Tracks the number of:
count OCBs using this attribute in any manner. When this count goes to zero, it means that no one is using this attribute.
rcount OCBs using this attribute for reading
wcount OCBs using this attribute for writing
rlocks Read locks currently registered on the attribute
wlocks Write locks currently registered on the attribute

These counts aren't exclusive. For example, if an OCB has specified that the resource is opened for reading and writing, then count, rcount, and wcount are all incremented. (See the iofunc_attr_init(), iofunc_lock_default(), iofunc_lock(), iofunc_ocb_attach(), and iofunc_ocb_detach() functions.)

The number of bytes in the resource; your resource manager can change this value.

For a file, this would contain the file's size. For special devices (e.g., /dev/null) that don't support lseek() or have a radically different interpretation for lseek(), this field isn't used (because you wouldn't use any of the helper functions, but would supply your own instead). In these cases, we recommend that you set this field to zero, unless there's a meaningful interpretation that you care to put to it.

The number of a mountpoint-specific inode that must be unique per mountpoint. You can specify your own value, or 0 to have the process manager fill it in for you. For filesystem type of applications, this may correspond to some on-disk structure. In any case, the interpretation of this field is up to you.
uid and gid
The user ID and group ID of the owner of this resource. These fields are updated automatically by the chown() helper functions (e.g., iofunc_chown_default()) and are referenced in conjunction with the mode member for access-granting purposes by the open() help functions (e.g., iofunc_open_default()).
mtime, atime, and ctime
POSIX time members:
  • mtime — modification time (write() updates this).
  • atime — access time (read() updates this).
  • ctime — change of status time (write(), chmod() and chown() update this).
Note: One or more of the three time members may be invalidated as a result of calling an iofunc-layer function. To see if a time member is invalid, check the flags member. This is to avoid having each and every I/O message handler go to the kernel and request the current time of day, just to fill in the attribute structure's time member(s).

POSIX states that these times must be valid when the fstat() is performed, but they don't have to reflect the actual time that the associated change occurred. Also, the times must be updated between fstat() invocations if the associated change occurred between fstat() invocations. If the associated change never occurred between fstat() invocations, then the time returned should be the same as returned last time. Furthermore, if the associated change occurred multiple times between fstat() invocations, then the time need only be different from the previously returned time.

To fill the members with the correct time, call iofunc_time_update().

The resource's mode (e.g., type, permissions). Valid modes may be selected from the S_* series of constants in <sys/stat.h>; see the entry for struct stat.
The number of links to this resource; your resource manager can modify this member. For resources that represent a directory, this value must be at least 2 (one for the directory itself, one for the ./ entry in it).
The device number for a character special device and the rdev number for a named special device.
mtime_ns, atime_ns, and ctime_ns
(QNX Neutrino 7.0 or later) The nanosecond values for the POSIX time members, mtime, atime, and ctime.

These fields are included if you compile for a 64-bit architecture, or if you define IOFUNC_NS_TIMESTAMP_SUPPORT before including <sys/iofunc.h> when you compile for a 32-bit architecture. If these fields are included, IOFUNC_ATTR_NS_TIMESTAMPS is set in the attribute's flags.


QNX Neutrino