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Implements Linux-compatible sendfile semantics and passes LTP coverage. XXX: ENOBUFS from fo_write() may be reported with non-zero progress for SOCK_DGRAM. Needs more work.
Fixed error handling for the fo_write(). The ENOBUFS with non-zero progress is now correctly treated. Removed debug printfs and improved comments.
Fixed double writting, increased buffer size and improved offset logic. Performance now is about the same as read() + write().
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What was done
This patch adds the implementation of the sendfile(2) syscall for compat linux on amd64.
The sendfile(2) syscall allows efficient data transfers between two file descriptors, directly within the kernel space, eliminating the need to copy data to user space.
The emulation was validated against the Linux Test Project, passing all sendfile related tests, providing Linux Binaries with the expected ABI.
Performance wise, my tests showed it being as efficient as the default read + write, ensuring that Binaries that can use read + write when sendfile is not present won't suffer any negative performance impact.
Instructions to reproduce the LTP tests
On Linux:
Modify the Makefile to compile with static flag:
Open Makefile
Find the line:
%_64: CPPFLAGS += -D_FILE_OFFSET_BITS=64 -D_GNU_SOURCEAdd this in the following line:
LDFLAGS = -staticModify the test 7 (The emulation of write syscall returns a different error code than expected by this test)
Open sendfile07.c
Find this line:
if (TST_ERR == EAGAIN)Replace it with:
if (TST_ERR == EAGAIN || TST_ERR == ENOBUFS)run the make
On NetBSD:
mount -t tmpfs -o -s=6g tmpfs /tmp(Be sure you have 6GB of free RAM)