问题
sendfile()
can be used to transmit data from a "file" descriptor to a "socket" descriptor in order to get data from machine A to machine B. Is it possible to get the data at the receiving end from the "socket" descriptor to a file with similar zero-copy semantics? I think sendfile()
doesn't help here because sendfile()
needs the source of data to be "page/buffer" cache. Is my understanding correct? Can splice()
help in this situation?
回答1:
You're correct about the limitation of sendfile
for this. And yes, splice
can help, but it's not trivial: splice
requires that at least one of the source or target file descriptors be a pipe. So you can't directly splice
from a socket to a plain file descriptor.
Conceptually, what you can do to make it work is:
- setup your inbound socket fd and your output file fd as you would normally
- create a pipe with pipe(2)
- in a loop:
- read from the socket to the write side of the pipe with splice
- write from the read side of the pipe to the file with
splice
also
Repeat the last steps until all the data is read.
Zero-Copy in Linux with sendfile() and splice() has an implementation of this technique.
来源:https://stackoverflow.com/questions/8626263/understanding-sendfile-and-splice