From a7ba1d42d0b09377aa7060158859febc292b2228 Mon Sep 17 00:00:00 2001 From: Florian Weimer Date: Fri, 31 Jan 2020 19:38:41 +0100 Subject: [PATCH] Update comment for the copy_file_range operation (#497) copy_file_range was first implemented with copy-based emulation in glibc 2.27, but the emulation was subsequently removed again because correct emulation depends on why the application attempted to make a copy. Therefore, file systems cannot rely on low-level userspace performing emulation. --- include/fuse.h | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/include/fuse.h b/include/fuse.h index 3df61b1..a92d5ee 100644 --- a/include/fuse.h +++ b/include/fuse.h @@ -772,9 +772,10 @@ struct fuse_operations { * additional cost of transferring data through the FUSE kernel module * to user space (glibc) and then back into the FUSE filesystem again. * - * In case this method is not implemented, glibc falls back to reading - * data from the source and writing to the destination. Effectively - * doing an inefficient copy of the data. + * In case this method is not implemented, applications are expected to + * fall back to a regular file copy. (Some glibc versions did this + * emulation automatically, but the emulation has been removed from all + * glibc release branches.) */ ssize_t (*copy_file_range) (const char *path_in, struct fuse_file_info *fi_in, -- 2.30.2