The sendfile *offset parameter refers to the input file offest, so it cannot be used in the same way as the copy_file_range *off_out parameter. Therefore, add sf_wrapper function which implements the *off_out behavior for sendfile.
Also update cfr_wrapper so that it does not rely on the fd_in file offset, and remove corresponding fd_in lseek calls which are no longer needed. The file offset of fd_in is now completely unused, except in the plain read/write loop, where lseek is called prior to entering the loop. Bug: https://bugs.gentoo.org/635126 --- [PATCH v5] eliminates all reliance on the file offset of fd_in, except in the plain read/write loop, where lseek is called prior to entering the loop. src/portage_util_file_copy_reflink_linux.c | 88 ++++++++++++++++++++---------- 1 file changed, 59 insertions(+), 29 deletions(-) diff --git a/src/portage_util_file_copy_reflink_linux.c b/src/portage_util_file_copy_reflink_linux.c index 4be9e0568..4c3303181 100644 --- a/src/portage_util_file_copy_reflink_linux.c +++ b/src/portage_util_file_copy_reflink_linux.c @@ -56,12 +56,18 @@ initreflink_linux(void) /** * cfr_wrapper - A copy_file_range syscall wrapper function, having a - * function signature that is compatible with sendfile. + * function signature that is compatible with sf_wrapper. * @fd_out: output file descriptor * @fd_in: input file descriptor - * @off_out: offset of the output file + * @off_out: must point to a buffer that specifies the starting offset + * where bytes will be copied to fd_out, and this buffer is adjusted by + * the number of bytes copied. * @len: number of bytes to copy between the file descriptors * + * Bytes are copied from fd_in starting from *off_out, and the file + * offset of fd_in is not changed. Effects on the file offset of + * fd_out are undefined. + * * Return: Number of bytes written to out_fd on success, -1 on failure * (errno is set appropriately). */ @@ -69,7 +75,8 @@ static ssize_t cfr_wrapper(int fd_out, int fd_in, off_t *off_out, size_t len) { #ifdef __NR_copy_file_range - return syscall(__NR_copy_file_range, fd_in, NULL, fd_out, + off_t off_in = *off_out; + return syscall(__NR_copy_file_range, fd_in, &off_in, fd_out, off_out, len, 0); #else /* This is how it fails at runtime when the syscall is not supported. */ @@ -79,18 +86,50 @@ cfr_wrapper(int fd_out, int fd_in, off_t *off_out, size_t len) } /** + * sf_wrapper - A sendfile wrapper function, having a function signature + * that is compatible with cfr_wrapper. + * @fd_out: output file descriptor + * @fd_in: input file descriptor + * @off_out: must point to a buffer that specifies the starting offset + * where bytes will be copied to fd_out, and this buffer is adjusted by + * the number of bytes copied. + * @len: number of bytes to copy between the file descriptors + * + * Bytes are copied from fd_in starting from *off_out, and the file + * offset of fd_in is not changed. Effects on the file offset of + * fd_out are undefined. + * + * Return: Number of bytes written to out_fd on success, -1 on failure + * (errno is set appropriately). + */ +static ssize_t +sf_wrapper(int fd_out, int fd_in, off_t *off_out, size_t len) +{ + ssize_t ret; + off_t off_in = *off_out; + /* The sendfile docs do not specify behavior of the output file + * offset, therefore it must be adjusted with lseek. + */ + if (lseek(fd_out, *off_out, SEEK_SET) < 0) + return -1; + ret = sendfile(fd_out, fd_in, &off_in, len); + if (ret > 0) + *off_out += ret; + return ret; +} + + +/** * do_lseek_data - Adjust file offsets to the next location containing * data, creating sparse empty blocks in the output file as needed. * @fd_in: input file descriptor * @fd_out: output file descriptor * @off_out: offset of the output file * - * Use lseek SEEK_DATA to adjust the fd_in file offset to the next - * location containing data, and adjust the fd_in file offset and - * off_out to the same location (creating sparse empty blocks as - * needed). On success, both fd_in and fd_out file offsets are - * guaranteed to be exactly equal to the value that off_out points to. - * + * Use lseek SEEK_DATA to adjust off_out to the next location from fd_in + * containing data (creates sparse empty blocks when appropriate). Effects + * on file offsets are undefined. + * * Return: On success, the number of bytes to copy before the next hole, * and -1 on failure (errno is set appropriately). Returns 0 when fd_in * reaches EOF. @@ -250,7 +289,7 @@ _reflink_linux_file_copy(PyObject *self, PyObject *args) * syscall is not available (less than Linux 4.5). */ error = 0; - copyfunc = sendfile; + copyfunc = sf_wrapper; copyfunc_ret = copyfunc(fd_out, fd_in, &offset_out, @@ -284,27 +323,18 @@ _reflink_linux_file_copy(PyObject *self, PyObject *args) } else { stat_in_acquired = 1; - /* For the sendfile call, the fd_in file offset must be - * exactly equal to offset_out. Use lseek to ensure - * correct state, in case an EINTR retry caused it to - * get out of sync somewhow. - */ - if (lseek(fd_in, offset_out, SEEK_SET) < 0) { - error = errno; - } else { - while (offset_out < stat_in.st_size) { - copyfunc_ret = sendfile(fd_out, - fd_in, - &offset_out, - stat_in.st_size - offset_out); + while (offset_out < stat_in.st_size) { + copyfunc_ret = sf_wrapper(fd_out, + fd_in, + &offset_out, + stat_in.st_size - offset_out); - if (copyfunc_ret < 0) { - error = errno; - if (errno == EINVAL && !offset_out) { - sendfile_works = 0; - } - break; + if (copyfunc_ret < 0) { + error = errno; + if (errno == EINVAL && !offset_out) { + sendfile_works = 0; } + break; } } } -- 2.13.5
