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Verify a client's read access to a resource
#include <sys/iofunc.h>
int iofunc_read_verify( resmgr_context_t* ctp,
io_read_t* msg,
iofunc_ocb_t* ocb,
int* nonblock );
- 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_read_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.
- nonblock
- NULL, or a pointer to a location where the function can
store a value that indicates whether or not the device is nonblocking:
- Nonzero — the client doesn't want to be blocked (i.e.
O_NONBLOCK was set).
- Zero — the client wants to be blocked.
libc
Use the -l c option to
qcc
to link against this library.
This library is usually included automatically.
The iofunc_read_verify() helper function checks that the client that
sent the _IO_READ message actually
has read access to the resource, and, if nonblock
isn't NULL, sets
nonblock to O_NONBLOCK or 0).
The read permission check is done against ocb->ioflag.
Note that the io_read_t message has an override flag
called msg->i.xtype.
This flag allows the client to override the default blocking
behavior for the resource on a per-request basis.
This override flag is checked, and returned in the
optional nonblock.
Note that if you're reading from a directory entry, you must
return
struct dirent
structures in the read
callout for your resource manager.
You'll also need to indicate how many bytes were read.
You can do this with the macro:
_IO_SET_READ_NBYTES( resmgr_context_t *ctp,
int nbytes )
The io_read_t structure holds the _IO_READ
message received by the resource manager:
struct _io_read {
uint16_t type;
uint16_t combine_len;
int32_t nbytes;
uint32_t xtype;
uint32_t zero;
};
typedef union {
struct _io_read i;
/* unsigned char data[nbytes]; */
/* nbytes is returned with MsgReply */
} io_read_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_read that
contains the following members:
- type
- _IO_READ.
- 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.
- nbytes
- The number of bytes that the client wants to read.
- xtype
- Extended type information; one of:
- _IO_XTYPE_NONE
- _IO_XTYPE_READCOND
- _IO_XTYPE_MQUEUE
- _IO_XTYPE_TCPIP
- _IO_XTYPE_TCPIP_MSG
- _IO_XTYPE_OFFSET
- _IO_XTYPE_REGISTRY
- _IO_XFLAG_DIR_EXTRA_HINT — this flag is valid only
when reading from a directory.
The filesystem should normally return extra directory information when
it's easy to get.
If this flag is set, it is a hint to the filesystem to try harder
(possibly causing media lookups) to return the extra information.
The most common use would be to return _DTYPE_LSTAT
information.
- _IO_XFLAG_NONBLOCK
- _IO_XFLAG_BLOCK
For more information, see
“Handling other read/write details”
in the Handling Read and Write Messages chapter of
Writing a Resource Manager.
The commented-out declaration for data indicates that
nbytes bytes of data immediately follow the
io_read_t structure.
- EOK
- The client has read access to this resource.
- EBADF
- The client doesn't have read access to this resource.
QNX Neutrino
Safety: | |
Cancellation point |
No |
Interrupt handler |
No |
Signal handler |
Yes |
Thread |
Yes |
dirent,
iofunc_open(),
iofunc_write_verify()
Writing a Resource Manager
Resource Managers
chapter of Getting Started with QNX Neutrino
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