//Linux really needs a clean basis for asynchronous and
//unbuffered i/o libraries. Something like the fork/thread
//clone(), but to replace select() and aio_* polling. This
//might be a start. And it is just a file and very like a
//pipe or socket.
//Suppose we add /dev/qio with 64 byte sectors as follows:
struct qio{ //64 byte i/o request
u16 flags; //0.0 request block variant, SEEK_SET...
u16 verb; //0.2 open,close,read,mmap,sync,write,
// ioctl
// mallocIO&read,write&freeIO,
// mallocIO,freeIO
// autothread might be an ioctl()
u16 errno; //0.4 per request status
u16 completehow; //0.6 queue,AST,pipe,SIGIO,SIGIO||delete ok
u64 offset; //1
u32 length; //2.0 bytes requested
u32 timeout; //2.4 im ms or us?
u32 transferred; //3.0 bytes
u32 qiohandle; //3.4 for cancell or polling
void* handle; //4 (open & close might write)
void* buffer; //5
void* callback; //6 optimize special cases w/ completehow
void* callparam; //7
}; //all fields are read xor write
//Writing to the device would schedule i/o, reading would reap
//completions. Bad writes would give the byte offset to the
//rejected sector field if detected synchronously. Multiple
//sector writes would be truncated on the first bad sector.
//Accepted writes would be buffered in the kernel.
//Each open creates a new queue, each write is read in the
//same queue. Any number of threads can read or write a queue.
//some cases might be simplified by kernel processed completions,
//such as VMS AST emulation, or putting results in a pipe. Hence
//completehow, which might use callback and callparam.
//timeout?
//canceling i/o?
//Sun aio emulation?
//VMS qio emulation?
//MS IOCP emulation?
//malloc()&free() safe across threads?
//Should O_DIRECT would error unless properly aligned etc.
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This archive was generated by hypermail 2b29 : Sun Apr 15 2001 - 21:00:19 EST