Even though it was only called for devices that have bs->sg set (which must be character devices), sg_get_max_segments looked at /sys/dev/block which only works for block devices.
On Linux the sg driver has its own way to provide the maximum number of iovecs in a scatter/gather list. --- block/file-posix.c | 11 +++++++++++ 1 file changed, 11 insertions(+) diff --git a/block/file-posix.c b/block/file-posix.c index e37a6bb8de..b348b37ccb 100644 --- a/block/file-posix.c +++ b/block/file-posix.c @@ -1198,6 +1198,17 @@ static int sg_get_max_segments(int fd, struct stat *st) int sysfd = -1; long max_segments; + if (S_ISCHR(st->st_mode)) { + if (ioctl(fd, SG_GET_SG_TABLESIZE, &ret) == 0) { + return ret; + } + return -EIO; + } + + if (!S_ISBLK(st->st_mode)) { + return -ENOTSUP; + } + sysfspath = g_strdup_printf("/sys/dev/block/%u:%u/queue/max_segments", major(st->st_rdev), minor(st->st_rdev)); sysfd = open(sysfspath, O_RDONLY); -- 2.30.1