Hi Bernd,
On 6/30/23 01:13, Bernd Schubert wrote:
On 6/29/23 10:17, Hao Xu wrote:
From: Hao Xu <howeyxu@xxxxxxxxxxx>
FOPEN_DIRECT_IO is usually set by fuse daemon to indicate need of strong
coherency, e.g. network filesystems. Thus shared mmap is disabled since
it leverages page cache and may write to it, which may cause
inconsistence. But FOPEN_DIRECT_IO can be used not for coherency but to
reduce memory footprint as well, e.g. reduce guest memory usage with
virtiofs. Therefore, add a new fuse init flag FUSE_DIRECT_IO_RELAX to
relax restrictions in that mode, currently, it allows shared mmap.
One thing to note is to make sure it doesn't break coherency in your
use case.
Signed-off-by: Hao Xu <howeyxu@xxxxxxxxxxx>
---
v1 -> v2:
make the new flag a fuse init one rather than a open flag since it's
not common that different files in a filesystem has different
strategy of shared mmap.
fs/fuse/file.c | 8 ++++++--
fs/fuse/fuse_i.h | 3 +++
fs/fuse/inode.c | 5 ++++-
include/uapi/linux/fuse.h | 1 +
4 files changed, 14 insertions(+), 3 deletions(-)
diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index bc4115288eec..871b66b54322 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -2478,14 +2478,18 @@ static const struct vm_operations_struct
fuse_file_vm_ops = {
static int fuse_file_mmap(struct file *file, struct vm_area_struct
*vma)
{
struct fuse_file *ff = file->private_data;
+ struct fuse_conn *fc = ff->fm->fc;
/* DAX mmap is superior to direct_io mmap */
if (FUSE_IS_DAX(file_inode(file)))
return fuse_dax_mmap(file, vma);
if (ff->open_flags & FOPEN_DIRECT_IO) {
- /* Can't provide the coherency needed for MAP_SHARED */
- if (vma->vm_flags & VM_MAYSHARE)
+ /* Can't provide the coherency needed for MAP_SHARED
+ * if FUSE_DIRECT_IO_RELAX isn't set.
+ */
+ if (!(ff->open_flags & fc->direct_io_relax) &&
+ vma->vm_flags & VM_MAYSHARE)
return -ENODEV;
I'm confused here, the idea was that open_flags do not need additional
flags? Why is this not just
sorry for this, seems I sent a WIP version by accident.., I'll fix it soon.
Thanks,
Hao
