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

From: George Hu <[email-masked]>
Date: Sat, 14 Feb 2026 17:21:59 +0800

On 2/13/26 11:36 PM, Chris Torek wrote:

> On Fri, Feb 13, 2026 at 4:47 AM George Hu <[email-masked]> 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 <[email-masked]>
>> ---
>>   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