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<a href="https://gitlab.com/mrblarg64">Brian Denton</a>
<a href="https://gitlab.com/gnutls/gnutls/-/issues/1580#note_2115433664">commented</a>:
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<p style="color: inherit; line-height: 1.5; margin: 0;">My understanding is that you pass a single fd to multiple gnutls_record_send_file in a multithreaded scenario.</p>
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<p dir="auto" style="color: #28272d; margin: 0 0 16px;" align="initial">Exactly!</p>
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<p style="color: inherit; line-height: 1.5; margin: 0;">What's your expectation on (not) advancing the fd? What is it rooted in, does sendfile(2) have guarantees on such multithreaded usage?</p>
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<p dir="auto" style="color: #28272d; margin: 0 0 16px;" align="initial">This is covered in the man page for sendfile() (see "If offset is not NULL"), since you know it is in section 2 and are still skeptical I went above and beyond and made a test program that can confirm the syscall works with multithreading (I can post a link here later today).</p>
<p dir="auto" style="color: #28272d; margin: 0 0 16px;" align="initial">What happens with gnutls is I was straceing my server to see if the async IO is working properly <a href="https://www.bernmern.ca/programs/linux/bernweb/" rel="nofollow noreferrer noopener" target="_blank" style="margin-top: 0;">https://www.bernmern.ca/programs/linux/bernweb/</a> and noticed read() and lseek() syscalls originating from gnutls().</p>
<p dir="auto" style="color: #28272d; margin: 0 0 16px;" align="initial">I expect gnutls_record_send_file() to work like sendfile(), and like the documentation implies:</p>
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<p style="color: inherit; line-height: 1.5; margin: 0;">If offset is NULL then file offset is incremented by number of bytes send, otherwise file offset remains unchanged.
<a href="https://www.gnutls.org/reference/gnutls-gnutls.html#gnutls-record-send-file" rel="nofollow noreferrer noopener" target="_blank" style="margin-top: 0;">https://www.gnutls.org/reference/gnutls-gnutls.html#gnutls-record-send-file</a></p>
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