Verify a client's write access to a resource
#include <sys/iofunc.h> int iofunc_write_verify( resmgr_context_t* ctp, io_write_t* msg, iofunc_ocb_t* ocb, int* nonblock );
libc
Use the -l c option to qcc to link against this library. This library is usually included automatically.
The iofunc_write_verify() function checks that the client that sent the _IO_WRITE or _IO_WRITE64 message actually has write access to the resource, and, optionally (if nonblock isn't NULL), sets nonblock to O_NONBLOCK or 0.
The write permission check is done against ocb->ioflag.
Note that the io_write_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.
In the write callout for your resource manager, you'll need to indicate how many bytes were written. You can do this with the macro:
_IO_SET_WRITE_NBYTES( resmgr_context_t *ctp, int nbytes )
io_write_t structure
The io_write_t structure holds the _IO_WRITE or _IO_WRITE64 message received by the resource manager:
struct _io_write { uint16_t type; uint16_t combine_len; uint32_t nbytes; uint32_t xtype; uint32_t zero; /* unsigned char data[nbytes]; */ }; struct _io_write64 { uint16_t type; uint16_t combine_len; uint32_t nbytes; uint32_t xtype; uint32_t nbytes_hi; /* unsigned char data[nbytes]; */ }; typedef union { struct _io_write i; struct _io_write i64; /* nbytes is returned with MsgReply */ } io_write_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 or i64, that contains the following members:
if ((msg->i.xtype & _IO_XTYPE_MASK) == ...)
The relevant types include the following:
The xtype member doesn't include any useful flags.
For more information, see Handling other read/write details in the Handling Read and Write Messages chapter of Writing a Resource Manager.
num_bytes = _IO_WRITE_GET_NBYTES(msg);
The commented-out declaration for data indicates that nbytes bytes of data immediately follow the _io_write structure.
Safety: | |
---|---|
Cancellation point | No |
Interrupt handler | No |
Signal handler | No |
Thread | Yes |