[PATCH 17/17] fuse2fs: enable atomic writes

Darrick J. Wong
2025-09-16T01:03:11Z

Advertise the single-fsblock atomic write capability that iomap can do.

Signed-off-by: "Darrick J. Wong" <djwong@kernel.org>
---
fuse4fs/fuse4fs.c | 67 +++++++++++++++++++++++++++++++++++++++++++++++++++-
misc/fuse2fs.c | 68 ++++++++++++++++++++++++++++++++++++++++++++++++++++-
2 files changed, 133 insertions(+), 2 deletions(-)

diff --git a/fuse4fs/fuse4fs.c b/fuse4fs/fuse4fs.c
index 6c3e2992a04211..abbc67bccef786 100644
--- a/fuse4fs/fuse4fs.c
+++ b/fuse4fs/fuse4fs.c
@@ -278,6 +278,9 @@ struct fuse4fs {
void (*old_alloc_stats)(ext2_filsys fs, blk64_t blk, int inuse);
void (*old_alloc_stats_range)(ext2_filsys fs, blk64_t blk, blk_t num,
int inuse);
+#ifdef STATX_WRITE_ATOMIC
+ unsigned int awu_min, awu_max;
+#endif
#endif
unsigned int blockmask;
unsigned long offset;
@@ -736,8 +739,20 @@ static inline int fuse4fs_iomap_enabled(const struct fuse4fs *ff)
{
return ff->iomap_state >= IOMAP_ENABLED;
}
+
+static inline int fuse4fs_iomap_can_hw_atomic(const struct fuse4fs *ff)
+{
+ return fuse4fs_iomap_enabled(ff) &&
+ (ff->iomap_cap & FUSE_IOMAP_SUPPORT_ATOMIC) &&
+#ifdef STATX_WRITE_ATOMIC
+ ff->awu_min > 0 && ff->awu_min > 0;
+#else
+ 0;
+#endif
+}
#else
# define fuse4fs_iomap_enabled(...) (0)
+# define fuse4fs_iomap_can_hw_atomic(...) (0)
#endif

static inline void fuse4fs_dump_extents(struct fuse4fs *ff, ext2_ino_t ino,
@@ -1757,8 +1772,12 @@ static int fuse4fs_stat_inode(struct fuse4fs *ff, ext2_ino_t ino,

fstat->iflags = 0;
#ifdef HAVE_FUSE_IOMAP
- if (fuse4fs_iomap_enabled(ff))
+ if (fuse4fs_iomap_enabled(ff)) {
fstat->iflags |= FUSE_IFLAG_IOMAP;
+
+ if (fuse4fs_iomap_can_hw_atomic(ff))
+ fstat->iflags |= FUSE_IFLAG_ATOMIC;
+ }
#endif

return 0;
@@ -1933,6 +1952,15 @@ static int fuse4fs_statx(struct fuse4fs *ff, ext2_ino_t ino, int statx_mask,

fuse4fs_statx_directio(ff, stx);

+#ifdef STATX_WRITE_ATOMIC
+ if (fuse4fs_iomap_can_hw_atomic(ff)) {
+ stx->stx_mask |= STATX_WRITE_ATOMIC;
+ stx->stx_atomic_write_unit_min = ff->awu_min;
+ stx->stx_atomic_write_unit_max = ff->awu_max;
+ stx->stx_atomic_write_segments_max = 1;
+ }
+#endif
+
return 0;
}

@@ -6255,6 +6283,9 @@ static void op_iomap_begin(fuse_req_t req, fuse_ino_t fino, uint64_t dontcare,
}
}

+ if (opflags & FUSE_IOMAP_OP_ATOMIC)
+ read.flags |= FUSE_IOMAP_F_ATOMIC_BIO;
+
out_unlock:
fuse4fs_finish(ff, ret);
if (ret)
@@ -6419,6 +6450,38 @@ static int fuse4fs_set_bdev_blocksize(struct fuse4fs *ff, int fd)
return -EIO;
}

+#ifdef STATX_WRITE_ATOMIC
+static void fuse4fs_configure_atomic_write(struct fuse4fs *ff, int bdev_fd)
+{
+ struct statx devx;
+ unsigned int awu_min, awu_max;
+ int ret;
+
+ if (!ext2fs_has_feature_extents(ff->fs->super))
+ return;
+
+ ret = statx(bdev_fd, "", AT_EMPTY_PATH, STATX_WRITE_ATOMIC, &devx);
+ if (ret)
+ return;
+ if (!(devx.stx_mask & STATX_WRITE_ATOMIC))
+ return;
+
+ awu_min = max(ff->fs->blocksize, devx.stx_atomic_write_unit_min);
+ awu_max = min(ff->fs->blocksize, devx.stx_atomic_write_unit_max);
+ if (awu_min > awu_max)
+ return;
+
+ log_printf(ff, "%s awu_min: %u, awu_max: %u\n",
+ _("Supports (experimental) DIO atomic writes"),
+ awu_min, awu_max);
+
+ ff->awu_min = awu_min;
+ ff->awu_max = awu_max;
+}
+#else
+# define fuse4fs_configure_atomic_write(...) ((void)0)
+#endif
+
static int fuse4fs_iomap_config_devices(struct fuse4fs *ff)
{
errcode_t err;
@@ -6443,6 +6506,8 @@ static int fuse4fs_iomap_config_devices(struct fuse4fs *ff)
dbg_printf(ff, "%s: registered iomap dev fd=%d iomap_dev=%u\n",
__func__, fd, ff->iomap_dev);

+ fuse4fs_configure_atomic_write(ff, fd);
+
ff->iomap_dev = ret;
return 0;
}
diff --git a/misc/fuse2fs.c b/misc/fuse2fs.c
index d6bf7357653acd..0832a758bdad79 100644
--- a/misc/fuse2fs.c
+++ b/misc/fuse2fs.c
@@ -272,6 +272,9 @@ struct fuse2fs {
void (*old_alloc_stats)(ext2_filsys fs, blk64_t blk, int inuse);
void (*old_alloc_stats_range)(ext2_filsys fs, blk64_t blk, blk_t num,
int inuse);
+#ifdef STATX_WRITE_ATOMIC
+ unsigned int awu_min, awu_max;
+#endif
#endif
unsigned int blockmask;
unsigned long offset;
@@ -573,9 +576,21 @@ static inline int fuse2fs_iomap_enabled(const struct fuse2fs *ff)
{
return ff->iomap_state >= IOMAP_ENABLED;
}
+
+static inline int fuse2fs_iomap_can_hw_atomic(const struct fuse2fs *ff)
+{
+ return fuse2fs_iomap_enabled(ff) &&
+ (ff->iomap_cap & FUSE_IOMAP_SUPPORT_ATOMIC) &&
+#ifdef STATX_WRITE_ATOMIC
+ ff->awu_min > 0 && ff->awu_min > 0;
+#else
+ 0;
+#endif
+}
#else
# define fuse2fs_iomap_enabled(...) (0)
# define fuse2fs_iomap_enabled(...) (0)
+# define fuse2fs_iomap_can_hw_atomic(...) (0)
#endif

static inline void fuse2fs_dump_extents(struct fuse2fs *ff, ext2_ino_t ino,
@@ -1627,14 +1642,19 @@ static int op_getattr(const char *path, struct stat *statbuf,
static int op_getattr_iflags(const char *path, struct stat *statbuf,
unsigned int *iflags, struct fuse_file_info *fi)
{
+ struct fuse2fs *ff = fuse2fs_get();
int ret = op_getattr(path, statbuf, fi);

if (ret)
return ret;

- if (fuse_fs_can_enable_iomap(statbuf))
+ if (fuse_fs_can_enable_iomap(statbuf)) {
*iflags |= FUSE_IFLAG_IOMAP;

+ if (fuse2fs_iomap_can_hw_atomic(ff))
+ *iflags |= FUSE_IFLAG_ATOMIC;
+ }
+
return 0;
}
#endif
@@ -1740,6 +1760,15 @@ static int fuse2fs_statx(struct fuse2fs *ff, ext2_ino_t ino, int statx_mask,

fuse2fs_statx_directio(ff, stx);

+#ifdef STATX_WRITE_ATOMIC
+ if (fuse_fs_can_enable_iomapx(stx) && fuse2fs_iomap_can_hw_atomic(ff)) {
+ stx->stx_mask |= STATX_WRITE_ATOMIC;
+ stx->stx_atomic_write_unit_min = ff->awu_min;
+ stx->stx_atomic_write_unit_max = ff->awu_max;
+ stx->stx_atomic_write_segments_max = 1;
+ }
+#endif
+
return 0;
}

@@ -5783,6 +5812,9 @@ static int op_iomap_begin(const char *path, uint64_t nodeid, uint64_t attr_ino,
}
}

+ if (opflags & FUSE_IOMAP_OP_ATOMIC)
+ read->flags |= FUSE_IOMAP_F_ATOMIC_BIO;
+
out_unlock:
fuse2fs_finish(ff, ret);
return ret;
@@ -5944,6 +5976,38 @@ static int fuse2fs_set_bdev_blocksize(struct fuse2fs *ff, int fd)
return -EIO;
}

+#ifdef STATX_WRITE_ATOMIC
+static void fuse2fs_configure_atomic_write(struct fuse2fs *ff, int bdev_fd)
+{
+ struct statx devx;
+ unsigned int awu_min, awu_max;
+ int ret;
+
+ if (!ext2fs_has_feature_extents(ff->fs->super))
+ return;
+
+ ret = statx(bdev_fd, "", AT_EMPTY_PATH, STATX_WRITE_ATOMIC, &devx);
+ if (ret)
+ return;
+ if (!(devx.stx_mask & STATX_WRITE_ATOMIC))
+ return;
+
+ awu_min = max(ff->fs->blocksize, devx.stx_atomic_write_unit_min);
+ awu_max = min(ff->fs->blocksize, devx.stx_atomic_write_unit_max);
+ if (awu_min > awu_max)
+ return;
+
+ log_printf(ff, "%s awu_min: %u, awu_max: %u\n",
+ _("Supports (experimental) DIO atomic writes"),
+ awu_min, awu_max);
+
+ ff->awu_min = awu_min;
+ ff->awu_max = awu_max;
+}
+#else
+# define fuse2fs_configure_atomic_write(...) ((void)0)
+#endif
+
static int fuse2fs_iomap_config_devices(struct fuse2fs *ff)
{
errcode_t err;
@@ -5968,6 +6032,8 @@ static int fuse2fs_iomap_config_devices(struct fuse2fs *ff)
dbg_printf(ff, "%s: registered iomap dev fd=%d iomap_dev=%u\n",
__func__, fd, ff->iomap_dev);

+ fuse2fs_configure_atomic_write(ff, fd);
+
ff->iomap_dev = ret;
return 0;
}