[PATCH 2/2] erofs-utils: Enable 64-bit off_t with AC_SYS_LARGEFILE

[Gao Xiang]

Hi Jame,

On 2026/1/3 01:07, James Le Cuirot wrote:
> On Fri, Jan 02, 2026 at 03:38:31PM +0000, James Le Cuirot wrote:
>> I was initially just going go fix the += Bashism, but this is the safe
>> and portable way to enable 64-bit off_t. It is not possible to enable it
>> on some very old systems. erofs_off_t is hardcoded to u64, but I believe
>> this will still work correctly alongside a 32-bit off_t.
>>
>> Either way, you don't need HAVE_PREAD64 or HAVE_PWRITE64 because
>> pread64/pwrite64 are aliases of pread/pwrite when off_t is 64-bit. See
>> unistd.h and man pread(2).
>>
>> Signed-off-by: James Le Cuirot <chewi at gentoo.org>
>> ---
>>   configure.ac |  4 +---
>>   lib/io.c     | 20 +-------------------
>>   2 files changed, 2 insertions(+), 22 deletions(-)
>>
>> diff --git a/configure.ac b/configure.ac
>> index 4d34e1f..14332ed 100644
>> --- a/configure.ac
>> +++ b/configure.ac
>> @@ -251,8 +251,6 @@ AC_CHECK_FUNCS(m4_flatten([
>>   	lsetxattr
>>   	memset
>>   	realpath
>> -	pread64
>> -	pwrite64
>>   	pwritev
>>   	posix_fadvise
>>   	fstatfs
>> @@ -554,7 +552,7 @@ AS_IF([test "x$with_xxhash" != "xno"], [
>>   ])
>>   
>>   # Enable 64-bit off_t
>> -CFLAGS+=" -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64"
>> +AC_SYS_LARGEFILE
>>   
>>   # Configure fuzzing mode
>>   AS_IF([test "x$enable_fuzzing" != "xyes"], [], [
>> diff --git a/lib/io.c b/lib/io.c
>> index aa043ca..eaa5fa7 100644
>> --- a/lib/io.c
>> +++ b/lib/io.c
>> @@ -74,11 +74,7 @@ ssize_t erofs_io_pwrite(struct erofs_vfile *vf, const void *buf,
>>   
>>   	pos += vf->offset;
>>   	do {
>> -#ifdef HAVE_PWRITE64
>> -		ret = pwrite64(vf->fd, buf, len, (off64_t)pos);
>> -#else
>>   		ret = pwrite(vf->fd, buf, len, (off_t)pos);
>> -#endif
>>   		if (ret <= 0) {
>>   			if (!ret)
>>   				break;
>> @@ -208,11 +204,7 @@ ssize_t erofs_io_pread(struct erofs_vfile *vf, void *buf, u64 pos, size_t len)
>>   
>>   	pos += vf->offset;
>>   	do {
>> -#ifdef HAVE_PREAD64
>> -		ret = pread64(vf->fd, buf, len, (off64_t)pos);
>> -#else
>>   		ret = pread(vf->fd, buf, len, (off_t)pos);
>> -#endif
>>   		if (ret <= 0) {
>>   			if (!ret)
>>   				break;
>> @@ -436,11 +428,7 @@ static ssize_t __erofs_copy_file_range(int fd_in, u64 *off_in,
>>   		char *end, *p;
>>   
>>   		to_read = min_t(size_t, length, sizeof(buf));
>> -#ifdef HAVE_PREAD64
>> -		read_count = pread64(fd_in, buf, to_read, *off_in);
>> -#else
>>   		read_count = pread(fd_in, buf, to_read, *off_in);
>> -#endif
>>   		if (read_count == 0)
>>   			/* End of file reached prematurely. */
>>   			return copied;
>> @@ -455,13 +443,7 @@ static ssize_t __erofs_copy_file_range(int fd_in, u64 *off_in,
>>   		/* Write the buffer part which was read to the destination. */
>>   		end = buf + read_count;
>>   		for (p = buf; p < end; ) {
>> -			ssize_t write_count;
>> -
>> -#ifdef HAVE_PWRITE64
>> -			write_count = pwrite64(fd_out, p, end - p, *off_out);
>> -#else
>> -			write_count = pwrite(fd_out, p, end - p, *off_out);
>> -#endif
>> +			ssize_t write_count = pwrite(fd_out, p, end - p, *off_out);
>>   			if (write_count < 0) {
>>   				/*
>>   				 * Adjust the input read position to match what
>> -- 
>> 2.51.2
>>
> 
> Unfortunately, it's been pointed out to me that this change isn't safe because
> the config.h generated by configure is not consistently included everywhere.
> That could be fixed, but I don't feel like untangling that myself.

Sorry for late response.

Yes, currently config.h is not used everywhere, so it's still
perferred to use CFLAGS for now.

Thanks,
Gao Xiang