Re: [PATCH] copy.c: use `sendfile()` for in-kernel file copying on Linux

From: Chris Torek <chris.torek@gmail.com>
Date: Feb 14, 2026, 16:50 UTC
Message-ID: <CAPx1GvcdFN5gn97xxuNLRBy2sV2gK3Wm56Pw3tQGENN8_+BKnw@mail.gmail.com>
In-Reply-To: <e2a5c920-7f15-4ea8-9390-cf42ac33082d@archlinux.org>

Ah, more importantly, FreeBSD's sendfile only operates on sockets.

Both systems also need fallback code for un-handled cases.

Chris

On Sat, Feb 14, 2026 at 1:22 AM George Hu <integral@archlinux.org> wrote:

Show 43 quoted lines

>
> On 2/13/26 11:36 PM, Chris Torek wrote:
>
> > On Fri, Feb 13, 2026 at 4:47 AM George Hu <integral@archlinux.org> wrote:
> >> The `sendfile()` system call copies data between one file descriptor
> >> and another within the kernel, which is more efficient than the
> >> combination of `read()` and `write()`.
> > sendfile() is found on other systems (notably BSDs), so perhaps ...
> >
> >> Signed-off-by: George Hu <integral@archlinux.org>
> >> ---
> >>   copy.c | 17 +++++++++++++++++
> >>   1 file changed, 17 insertions(+)
> >>
> >> diff --git a/copy.c b/copy.c
> >> index b668209b6c..d4b7cde764 100644
> >> --- a/copy.c
> >> +++ b/copy.c
> >> @@ -7,8 +7,23 @@
> >>   #include "strbuf.h"
> >>   #include "abspath.h"
> >>
> >> +#ifdef __linux__
> > ... this and the subsequent ifdef should be based on the feature,
> > rather than the OS.
> >
> > Chris
>
> Hello,
>
> Although the `sendfile()` system call exists in both Linux and BSDs,
> their semantics and APIs differ.
> The Linux prototype of `sendfile()` is:
>
> ssize_t sendfile(int out_fd, int in_fd, off_t *_Nullable offset, size_t
> count);
>
> While FreeBSD exposes:
>
> int sendfile(int fd, int s, off_t offset, size_t nbytes, struct sf_hdtr
> *hdtr, off_t *sbytes, int flags);
>
> George