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Message-ID: <CAJnrk1ZDeYytdjuCdg6-O-PGjcmwS33LOnfFT_YY9SPE=x=Qxw@mail.gmail.com>
Date: Wed, 21 Jan 2026 17:13:39 -0800
From: Joanne Koong <joannelkoong@...il.com>
To: "Darrick J. Wong" <djwong@...nel.org>
Cc: miklos@...redi.hu, bernd@...ernd.com, neal@...pa.dev,
linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 07/31] fuse: create a per-inode flag for toggling iomap
On Tue, Oct 28, 2025 at 5:46 PM Darrick J. Wong <djwong@...nel.org> wrote:
>
> From: Darrick J. Wong <djwong@...nel.org>
>
> Create a per-inode flag to control whether or not this inode actually
> uses iomap. This is required for non-regular files because iomap
> doesn't apply there; and enables fuse filesystems to provide some
> non-iomap files if desired.
>
> Signed-off-by: "Darrick J. Wong" <djwong@...nel.org>
The logic in this makes sense to me, left just a few comments below.
Reviewed-by: Joanne Koong <joannelkoong@...il.com>
> ---
> fs/fuse/fuse_i.h | 17 ++++++++++++++++
> include/uapi/linux/fuse.h | 3 +++
> fs/fuse/file.c | 1 +
> fs/fuse/file_iomap.c | 49 +++++++++++++++++++++++++++++++++++++++++++++
> fs/fuse/inode.c | 26 ++++++++++++++++++------
> 5 files changed, 90 insertions(+), 6 deletions(-)
>
>
> diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
> index 839d4f2ada4656..c7aeb324fe599e 100644
> --- a/fs/fuse/fuse_i.h
> +++ b/fs/fuse/fuse_i.h
> @@ -257,6 +257,8 @@ enum {
> * or the fuse server has an exclusive "lease" on distributed fs
> */
> FUSE_I_EXCLUSIVE,
> + /* Use iomap for this inode */
> + FUSE_I_IOMAP,
> };
>
> struct fuse_conn;
> @@ -1717,11 +1719,26 @@ extern const struct fuse_backing_ops fuse_iomap_backing_ops;
>
> void fuse_iomap_mount(struct fuse_mount *fm);
> void fuse_iomap_unmount(struct fuse_mount *fm);
> +
> +void fuse_iomap_init_reg_inode(struct inode *inode, unsigned attr_flags);
> +void fuse_iomap_init_nonreg_inode(struct inode *inode, unsigned attr_flags);
> +void fuse_iomap_evict_inode(struct inode *inode);
> +
> +static inline bool fuse_inode_has_iomap(const struct inode *inode)
> +{
> + const struct fuse_inode *fi = get_fuse_inode(inode);
> +
> + return test_bit(FUSE_I_IOMAP, &fi->state);
> +}
> #else
> # define fuse_iomap_enabled(...) (false)
> # define fuse_has_iomap(...) (false)
> # define fuse_iomap_mount(...) ((void)0)
> # define fuse_iomap_unmount(...) ((void)0)
> +# define fuse_iomap_init_reg_inode(...) ((void)0)
> +# define fuse_iomap_init_nonreg_inode(...) ((void)0)
> +# define fuse_iomap_evict_inode(...) ((void)0)
> +# define fuse_inode_has_iomap(...) (false)
> #endif
>
> #endif /* _FS_FUSE_I_H */
> diff --git a/include/uapi/linux/fuse.h b/include/uapi/linux/fuse.h
> index e571f8ceecbfad..e949bfe022c3b0 100644
> --- a/include/uapi/linux/fuse.h
> +++ b/include/uapi/linux/fuse.h
> @@ -243,6 +243,7 @@
> *
> * 7.99
> * - add FUSE_IOMAP and iomap_{begin,end,ioend} for regular file operations
> + * - add FUSE_ATTR_IOMAP to enable iomap for specific inodes
> */
>
> #ifndef _LINUX_FUSE_H
> @@ -583,9 +584,11 @@ struct fuse_file_lock {
> *
> * FUSE_ATTR_SUBMOUNT: Object is a submount root
> * FUSE_ATTR_DAX: Enable DAX for this file in per inode DAX mode
> + * FUSE_ATTR_IOMAP: Use iomap for this inode
> */
> #define FUSE_ATTR_SUBMOUNT (1 << 0)
> #define FUSE_ATTR_DAX (1 << 1)
> +#define FUSE_ATTR_IOMAP (1 << 2)
>
> /**
> * Open flags
> diff --git a/fs/fuse/file.c b/fs/fuse/file.c
> index f1ef77a0be05bb..42c85c19f3b13b 100644
> --- a/fs/fuse/file.c
> +++ b/fs/fuse/file.c
> @@ -3135,6 +3135,7 @@ void fuse_init_file_inode(struct inode *inode, unsigned int flags)
> init_waitqueue_head(&fi->page_waitq);
> init_waitqueue_head(&fi->direct_io_waitq);
>
> + fuse_iomap_init_reg_inode(inode, flags);
imo it's a bit confusing to have this here when the rest of the
fuse_iomap_init_nonreg_inode() calls happen inside the switch case
statement. Maybe it makes sense to have this inside the switch case
like the fuse_iomap_init_nonreg_inode() calls, or alternatively move
the fuse_iomap_init_nonreg_inode() calls into their corresponding
helpers (eg fuse_init_dir(), etc.), so that it's consistent?
> if (IS_ENABLED(CONFIG_FUSE_DAX))
> fuse_dax_inode_init(inode, flags);
> }
> diff --git a/fs/fuse/file_iomap.c b/fs/fuse/file_iomap.c
> index 1b9e1bf2f799a3..fc0d5f135bacf9 100644
> --- a/fs/fuse/file_iomap.c
> +++ b/fs/fuse/file_iomap.c
> @@ -635,3 +635,52 @@ void fuse_iomap_unmount(struct fuse_mount *fm)
> fuse_flush_requests_and_wait(fc);
> fuse_send_destroy(fm);
> }
> +
> +static inline void fuse_inode_set_iomap(struct inode *inode)
> +{
> + struct fuse_inode *fi = get_fuse_inode(inode);
> +
> + set_bit(FUSE_I_IOMAP, &fi->state);
> +}
> +
> +static inline void fuse_inode_clear_iomap(struct inode *inode)
> +{
> + struct fuse_inode *fi = get_fuse_inode(inode);
> +
> + clear_bit(FUSE_I_IOMAP, &fi->state);
> +}
> +
> +void fuse_iomap_init_nonreg_inode(struct inode *inode, unsigned attr_flags)
> +{
> + struct fuse_conn *conn = get_fuse_conn(inode);
> + struct fuse_inode *fi = get_fuse_inode(inode);
> +
> + ASSERT(!S_ISREG(inode->i_mode));
> +
> + if (conn->iomap && (attr_flags & FUSE_ATTR_IOMAP))
> + set_bit(FUSE_I_EXCLUSIVE, &fi->state);
> +}
> +
> +void fuse_iomap_init_reg_inode(struct inode *inode, unsigned attr_flags)
> +{
> + struct fuse_conn *conn = get_fuse_conn(inode);
> + struct fuse_inode *fi = get_fuse_inode(inode);
> +
> + ASSERT(S_ISREG(inode->i_mode));
> +
> + if (conn->iomap && (attr_flags & FUSE_ATTR_IOMAP)) {
> + set_bit(FUSE_I_EXCLUSIVE, &fi->state);
> + fuse_inode_set_iomap(inode);
> + }
> +}
> +
> +void fuse_iomap_evict_inode(struct inode *inode)
> +{
> + struct fuse_conn *conn = get_fuse_conn(inode);
> + struct fuse_inode *fi = get_fuse_inode(inode);
> +
> + if (fuse_inode_has_iomap(inode))
If I'm understanding this correctly, a fuse inode can't have
FUSE_I_IOMAP set on it if conn>iomap is not enabled, correct? Maybe it
makes sense to just return if (!conn->iomap) at the very beginning, to
make that more clear?
> + fuse_inode_clear_iomap(inode);
> + if (conn->iomap && fuse_inode_is_exclusive(inode))
> + clear_bit(FUSE_I_EXCLUSIVE, &fi->state);
> +}
> diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
> index 271356fa3be3ea..9b9e7b2dd0d928 100644
> --- a/fs/fuse/inode.c
> +++ b/fs/fuse/inode.c
> @@ -196,6 +196,8 @@ static void fuse_evict_inode(struct inode *inode)
> WARN_ON(!list_empty(&fi->write_files));
> WARN_ON(!list_empty(&fi->queued_writes));
> }
> +
> + fuse_iomap_evict_inode(inode);
> }
>
> static int fuse_reconfigure(struct fs_context *fsc)
> @@ -428,20 +430,32 @@ static void fuse_init_inode(struct inode *inode, struct fuse_attr *attr,
> inode->i_size = attr->size;
> inode_set_mtime(inode, attr->mtime, attr->mtimensec);
> inode_set_ctime(inode, attr->ctime, attr->ctimensec);
> - if (S_ISREG(inode->i_mode)) {
> + switch (inode->i_mode & S_IFMT) {
> + case S_IFREG:
> fuse_init_common(inode);
> fuse_init_file_inode(inode, attr->flags);
> - } else if (S_ISDIR(inode->i_mode))
> + break;
> + case S_IFDIR:
> fuse_init_dir(inode);
> - else if (S_ISLNK(inode->i_mode))
> + fuse_iomap_init_nonreg_inode(inode, attr->flags);
> + break;
> + case S_IFLNK:
> fuse_init_symlink(inode);
> - else if (S_ISCHR(inode->i_mode) || S_ISBLK(inode->i_mode) ||
> - S_ISFIFO(inode->i_mode) || S_ISSOCK(inode->i_mode)) {
> + fuse_iomap_init_nonreg_inode(inode, attr->flags);
> + break;
> + case S_IFCHR:
> + case S_IFBLK:
> + case S_IFIFO:
> + case S_IFSOCK:
> fuse_init_common(inode);
> init_special_inode(inode, inode->i_mode,
> new_decode_dev(attr->rdev));
> - } else
> + fuse_iomap_init_nonreg_inode(inode, attr->flags);
> + break;
> + default:
> BUG();
Just thinking out loud here and curious to hear whether you like this
idea or not: another option is calling
if (conn->iomap)
fuse_iomap_init_inode();
at the end, where fuse_iomap_init_inode() would be something like:
void fuse_iomap_init_inode(struct inode *inode, unsigned attr_flags)
{
struct fuse_inode *fi = get_fuse_inode(inode);
if (attr_flags & FUSE_ATTR_IOMAP)
set_bit(FUSE_I_EXCLUSIVE, &fi->state);
if (S_ISREG(inode->i_mode))
fuse_inode_set_iomap(inode);
}
which seems simpler to me than having both
fuse_iomap_init_nonreg_inode() and fuse_iomap_init_reg_inode()
function and invoking it per i_mode case.
Thanks,
Joanne
> + break;
> + }
> /*
> * Ensure that we don't cache acls for daemons without FUSE_POSIX_ACL
> * so they see the exact same behavior as before.
>
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