iofunc_chmod()

Handle an _IO_CHMOD message

Synopsis:

#include <sys/iofunc.h>

int iofunc_chmod ( resmgr_context_t *ctp,
                   io_chmod_t *msg,
                   iofunc_ocb_t *ocb,
                   iofunc_attr_t *attr );

Arguments:

ctp

A pointer to a resmgr_context_t structure that the resource-manager library uses to pass context information between functions.

msg

A pointer to the io_chmod_t structure that contains the message that the resource manager received; see below.

ocb

A pointer to the iofunc_ocb_t structure for the Open Control Block that was created when the client opened the resource.

attr

A pointer to the iofunc_attr_t structure that describes the characteristics of the device that's associated with your resource manager.

Library:

libc

Use the -l c option to qcc to link against this library. This library is usually included automatically.

Description:

The iofunc_chmod() helper function implements POSIX semantics for the client's chmod() call, which is received as an _IO_CHMOD message by the resource manager.

The iofunc_chmod() function verifies that the client has the necessary permissions to effect a chmod() on the attribute. If so, the chmod() is performed, modifying elements of the ocb->attr structure. This function takes care of updating the IOFUNC_ATTR_CTIME, IOFUNC_ATTR_DIRTY_TIME, and IOFUNC_ATTR_DIRTY_MODE bits in ocb->attr->flags. You can use iofunc_time_update(), to update the appropriate time fields in ocb->attr.

You can use iofunc_chmod(), for example, in a filesystem manager, where an _IO_CHMOD message was received, and the filesystem code must now write the values to the medium. The filesystem code may wish to block the client thread until the data was actually written to the medium. Contrast this scenario to the behavior of iofunc_chmod_default(), which calls this routine, and replies to the client thread.

io_chmod_t structure

The io_chmod_t structure holds the _IO_CHMOD message received by the resource manager:

struct _io_chmod {
    uint16_t                    type;
    uint16_t                    combine_len;
    mode_t                      mode;
};

typedef union {
    struct _io_chmod            i;
} io_chmod_t;

The I/O message structures are unions of an input message (coming to the resource manager) and an output or reply message (going back to the client). In this case, there's only an input message, i.

The i member is a structure of type _io_chmod that contains the following members:

type

_IO_CHMOD.

combine_len

If the message is a combine message, _IO_COMBINE_FLAG is set in this member. For more information, see Combine Messages chapter of Writing a Resource Manager.

mode

The new mode. For more information, see “Access permissions” in the documentation for stat().

Returns:

EOK

Successful completion.

EROFS

An attempt was made to chmod on a read-only filesystem.

EACCES

The client doesn't have permissions to do the operation.

EPERM

The group ID or owner ID didn't match.

Classification:

QNX Neutrino

See also:

iofunc_attr_t, iofunc_chmod_default(), iofunc_ocb_t, iofunc_time_update(), resmgr_context_t

Writing a Resource Manager

Resource Managers chapter of Getting Started with QNX Neutrino