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 );
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 or _IO_READ64 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 )
io_read_t structure
The io_read_t structure holds the _IO_READ or _IO_READ64 message received by the resource manager:
struct _io_read { uint16_t type; uint16_t combine_len; uint32_t nbytes; uint32_t xtype; uint32_t zero; }; struct _io_read64 { uint16_t type; uint16_t combine_len; uint32_t nbytes; uint32_t xtype; uint32_t nbytes_hi; }; typedef union { struct _io_read i; struct _io_read i64; /* 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 or i64, that contains the following members:
if ((msg->i.xtype & _IO_XTYPE_MASK) == ...)
The relevant types include the following:
The xtype member may also include the following 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_READ_GET_NBYTES(msg);
The commented-out declaration for data indicates that nbytes bytes of data immediately follow the io_read_t structure.
Safety: | |
---|---|
Cancellation point | No |
Interrupt handler | No |
Signal handler | Yes |
Thread | Yes |