Earlier quoted context omitted.
I don't honestly remember all of the write semantics - I thought it will only not report error if it gets interrupted by a signal handler after it wrote something. In case of true error, i thought it always return an error. write does have a weird error-checking semantic - you can get it to check for a bunch of errors without writing data by using a count of 0. At least as documented, sendfile does not have any of th…
As documented, sendfile (I haven't looked at whatever this "spliced_copy" is) does what Joker_vD said it should: if it does a partial write then it is considered "successful" and the caller is required to retry the call if less than the expected amount of data was sent.
Where is this documented?
man sendfile on my linux box doesn't even contain the word "partial", nor does it say what you said in some other way that i can see.