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Message-ID: <CAOQ4uxh80xhhPWTQOi8pTc2b3qveYcNkNV0-hsxh3p2u27nuUg@mail.gmail.com>
Date: Thu, 6 Nov 2025 19:44:46 +0100
From: Amir Goldstein <amir73il@...il.com>
To: "Darrick J. Wong" <djwong@...nel.org>
Cc: miklos@...redi.hu, joannelkoong@...il.com, bernd@...ernd.com,
neal@...pa.dev, linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 09/31] fuse: isolate the other regular file IO paths from iomap
On Wed, Oct 29, 2025 at 1:47 AM Darrick J. Wong <djwong@...nel.org> wrote:
>
> From: Darrick J. Wong <djwong@...nel.org>
>
> iomap completely takes over all regular file IO, so we don't need to
> access any of the other mechanisms at all. Gate them off so that we can
> eventually overlay them with a union to save space in struct fuse_inode.
>
> Signed-off-by: "Darrick J. Wong" <djwong@...nel.org>
> ---
I apologize for providing criticism which is not very productive.
Looking at this I don't feel much confidence to say that all cases are covered
and worse, I don't have much confidence that future coder won't easily
write some code that accesses the wrong side of the union.
I don't really have great ideas on how to improve.
Maybe at least some of the gates can be inside the _nowrite accessors?
Please don't take this as any sort of objection to this patch.
Thanks,
Amir.
> fs/fuse/dir.c | 14 +++++++++-----
> fs/fuse/file.c | 18 +++++++++++++-----
> fs/fuse/inode.c | 3 ++-
> fs/fuse/iomode.c | 2 +-
> 4 files changed, 25 insertions(+), 12 deletions(-)
>
>
> diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
> index 3c222b99d6e699..18eb1bb192bb58 100644
> --- a/fs/fuse/dir.c
> +++ b/fs/fuse/dir.c
> @@ -1991,6 +1991,7 @@ int fuse_do_setattr(struct mnt_idmap *idmap, struct dentry *dentry,
> FUSE_ARGS(args);
> struct fuse_setattr_in inarg;
> struct fuse_attr_out outarg;
> + const bool is_iomap = fuse_inode_has_iomap(inode);
> bool is_truncate = false;
> bool is_wb = fc->writeback_cache && S_ISREG(inode->i_mode);
> loff_t oldsize;
> @@ -2048,12 +2049,15 @@ int fuse_do_setattr(struct mnt_idmap *idmap, struct dentry *dentry,
> if (err)
> return err;
>
> - fuse_set_nowrite(inode);
> - fuse_release_nowrite(inode);
> + if (!is_iomap) {
> + fuse_set_nowrite(inode);
> + fuse_release_nowrite(inode);
> + }
> }
>
> if (is_truncate) {
> - fuse_set_nowrite(inode);
> + if (!is_iomap)
> + fuse_set_nowrite(inode);
> set_bit(FUSE_I_SIZE_UNSTABLE, &fi->state);
> if (trust_local_cmtime && attr->ia_size != inode->i_size)
> attr->ia_valid |= ATTR_MTIME | ATTR_CTIME;
> @@ -2125,7 +2129,7 @@ int fuse_do_setattr(struct mnt_idmap *idmap, struct dentry *dentry,
> if (!is_wb || is_truncate)
> i_size_write(inode, outarg.attr.size);
>
> - if (is_truncate) {
> + if (is_truncate && !is_iomap) {
> /* NOTE: this may release/reacquire fi->lock */
> __fuse_release_nowrite(inode);
> }
> @@ -2149,7 +2153,7 @@ int fuse_do_setattr(struct mnt_idmap *idmap, struct dentry *dentry,
> return 0;
>
> error:
> - if (is_truncate)
> + if (is_truncate && !is_iomap)
> fuse_release_nowrite(inode);
>
> clear_bit(FUSE_I_SIZE_UNSTABLE, &fi->state);
> diff --git a/fs/fuse/file.c b/fs/fuse/file.c
> index 42c85c19f3b13b..bd9c208a46c78d 100644
> --- a/fs/fuse/file.c
> +++ b/fs/fuse/file.c
> @@ -238,6 +238,7 @@ static int fuse_open(struct inode *inode, struct file *file)
> struct fuse_conn *fc = fm->fc;
> struct fuse_file *ff;
> int err;
> + const bool is_iomap = fuse_inode_has_iomap(inode);
> bool is_truncate = (file->f_flags & O_TRUNC) && fc->atomic_o_trunc;
> bool is_wb_truncate = is_truncate && fc->writeback_cache;
> bool dax_truncate = is_truncate && FUSE_IS_DAX(inode);
> @@ -259,7 +260,7 @@ static int fuse_open(struct inode *inode, struct file *file)
> goto out_inode_unlock;
> }
>
> - if (is_wb_truncate || dax_truncate)
> + if ((is_wb_truncate || dax_truncate) && !is_iomap)
> fuse_set_nowrite(inode);
>
> err = fuse_do_open(fm, get_node_id(inode), file, false);
> @@ -272,7 +273,7 @@ static int fuse_open(struct inode *inode, struct file *file)
> fuse_truncate_update_attr(inode, file);
> }
>
> - if (is_wb_truncate || dax_truncate)
> + if ((is_wb_truncate || dax_truncate) && !is_iomap)
> fuse_release_nowrite(inode);
> if (!err) {
> if (is_truncate)
> @@ -520,12 +521,14 @@ static int fuse_fsync(struct file *file, loff_t start, loff_t end,
> {
> struct inode *inode = file->f_mapping->host;
> struct fuse_conn *fc = get_fuse_conn(inode);
> + const bool need_sync_writes = !fuse_inode_has_iomap(inode);
> int err;
>
> if (fuse_is_bad(inode))
> return -EIO;
>
> - inode_lock(inode);
> + if (need_sync_writes)
> + inode_lock(inode);
>
> /*
> * Start writeback against all dirty pages of the inode, then
> @@ -536,7 +539,8 @@ static int fuse_fsync(struct file *file, loff_t start, loff_t end,
> if (err)
> goto out;
>
> - fuse_sync_writes(inode);
> + if (need_sync_writes)
> + fuse_sync_writes(inode);
>
> /*
> * Due to implementation of fuse writeback
> @@ -560,7 +564,8 @@ static int fuse_fsync(struct file *file, loff_t start, loff_t end,
> err = 0;
> }
> out:
> - inode_unlock(inode);
> + if (need_sync_writes)
> + inode_unlock(inode);
>
> return err;
> }
> @@ -1942,6 +1947,9 @@ static struct fuse_file *__fuse_write_file_get(struct fuse_inode *fi)
> {
> struct fuse_file *ff;
>
> + if (fuse_inode_has_iomap(&fi->inode))
> + return NULL;
> +
> spin_lock(&fi->lock);
> ff = list_first_entry_or_null(&fi->write_files, struct fuse_file,
> write_entry);
> diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
> index 9b9e7b2dd0d928..7602595006a19d 100644
> --- a/fs/fuse/inode.c
> +++ b/fs/fuse/inode.c
> @@ -191,7 +191,8 @@ static void fuse_evict_inode(struct inode *inode)
> if (inode->i_nlink > 0)
> atomic64_inc(&fc->evict_ctr);
> }
> - if (S_ISREG(inode->i_mode) && !fuse_is_bad(inode)) {
> + if (S_ISREG(inode->i_mode) && !fuse_is_bad(inode) &&
> + !fuse_inode_has_iomap(inode)) {
> WARN_ON(fi->iocachectr != 0);
> WARN_ON(!list_empty(&fi->write_files));
> WARN_ON(!list_empty(&fi->queued_writes));
> diff --git a/fs/fuse/iomode.c b/fs/fuse/iomode.c
> index 3728933188f307..0a534e5a6db5f6 100644
> --- a/fs/fuse/iomode.c
> +++ b/fs/fuse/iomode.c
> @@ -203,7 +203,7 @@ int fuse_file_io_open(struct file *file, struct inode *inode)
> * io modes are not relevant with DAX and with server that does not
> * implement open.
> */
> - if (FUSE_IS_DAX(inode) || !ff->args)
> + if (fuse_inode_has_iomap(inode) || FUSE_IS_DAX(inode) || !ff->args)
> return 0;
>
> /*
>
>
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