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下面是The Open Group Base Specifications Issue 6里对write的部分说明
If the value of nbyte is greater than {SSIZE_MAX}, the result is implementation-defined.
After a write() to a regular file has successfully returned:
Any successful read() from each byte position in the file that was modified by that write shall return the data specified by the write() for that position until such byte positions are again modified.
Any subsequent successful write() to the same byte position in the file shall overwrite that file data.
Write requests to a pipe or FIFO shall be handled in the same way as a regular file with the following exceptions:
There is no file offset associated with a pipe, hence each write request shall append to the end of the pipe.
Write requests of {PIPE_BUF} bytes or less shall not be interleaved with data from other processes doing writes on the same pipe. Writes of greater than {PIPE_BUF} bytes may have data interleaved, on arbitrary boundaries, with writes by other processes, whether or not the O_NONBLOCK flag of the file status flags is set.
If the O_NONBLOCK flag is clear, a write request may cause the thread to block, but on normal completion it shall return nbyte.
If the O_NONBLOCK flag is set, write() requests shall be handled differently, in the following ways:
The write() function shall not block the thread.
A write request for {PIPE_BUF} or fewer bytes shall have the following effect: if there is sufficient space available in the pipe, write() shall transfer all the data and return the number of bytes requested. Otherwise, write() shall transfer no data and return -1 with errno set to [EAGAIN].
A write request for more than {PIPE_BUF} bytes shall cause one of the following:
When at least one byte can be written, transfer what it can and return the number of bytes written. When all data previously written to the pipe is read, it shall transfer at least {PIPE_BUF} bytes.
When no data can be written, transfer no data, and return -1 with errno set to [EAGAIN].
When attempting to write to a file descriptor (other than a pipe or FIFO) that supports non-blocking writes and cannot accept the data immediately:
If the O_NONBLOCK flag is clear, write() shall block the calling thread until the data can be accepted.
If the O_NONBLOCK flag is set, write() shall not block the thread. If some data can be written without blocking the thread, write() shall write what it can and return the number of bytes written. Otherwise, it shall return -1 and set errno to [EAGAIN].
Upon successful completion, where nbyte is greater than 0, write() shall mark for update the st_ctime and st_mtime fields of the file, and if the file is a regular file, the S_ISUID and S_ISGID bits of the file mode may be cleared.
For regular files, no data transfer shall occur past the offset maximum established in the open file description associated with fildes. |
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发表于 2006-09-17 23:48
发表于 2006-09-18 20:19
