On Fri, Feb 12, 2021 at 12:44:05PM +0800, Nicolas Boichat wrote: > copy_file_range (which calls generic_copy_file_checks) uses the > inode file size to adjust the copy count parameter. This breaks > with special filesystems like procfs/sysfs/debugfs/tracefs, where > the file size appears to be zero, but content is actually returned > when a read operation is performed. Other issues would also > happen on partial writes, as the function would attempt to seek > in the input file. > > Use the newly introduced FS_GENERATED_CONTENT filesystem flag > to return -EOPNOTSUPP: applications can then retry with a more > usual read/write based file copy (the fallback code is usually > already present to handle older kernels). > > Signed-off-by: Nicolas Boichat <[email protected]> > --- > > fs/read_write.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/fs/read_write.c b/fs/read_write.c > index 0029ff2b0ca8..80322e89fb0a 100644 > --- a/fs/read_write.c > +++ b/fs/read_write.c > @@ -1485,6 +1485,9 @@ ssize_t vfs_copy_file_range(struct file *file_in, > loff_t pos_in, > if (flags != 0) > return -EINVAL; > > + if (file_inode(file_in)->i_sb->s_type->fs_flags & FS_GENERATED_CONTENT) > + return -EOPNOTSUPP;
Why not declare a dummy copy_file_range_nop function that returns EOPNOTSUPP and point all of these filesystems at it? (Or, I guess in these days where function pointers are the enemy, create a #define that is a cast of 0x1, and fix do_copy_file_range to return EOPNOTSUPP if it sees that?) --D > + > ret = generic_copy_file_checks(file_in, pos_in, file_out, pos_out, &len, > flags); > if (unlikely(ret)) > -- > 2.30.0.478.g8a0d178c01-goog >
