Messages in this thread | | | Date | Thu, 12 Apr 2001 08:40:15 -0700 | From | CJ <> | Subject | Asynchronous io |
| |
//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. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |