[PATCH 26/52] fuse: Implement basic DAX read/write support commands

From: Vivek Goyal
Date: Mon Dec 10 2018 - 12:18:01 EST

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From: Stefan Hajnoczi <stefanha@xxxxxxxxxx>

This patch implements basic DAX support. mmap() is not implemented
yet and will come in later patches. This patch looks into implemeting
read/write.

Signed-off-by: Stefan Hajnoczi <stefanha@xxxxxxxxxx>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@xxxxxxxxxx>
Signed-off-by: Vivek Goyal <vgoyal@xxxxxxxxxx>
---
fs/fuse/file.c | 400 ++++++++++++++++++++++++++++++++++++++++++++++
fs/fuse/fuse_i.h | 6 +
fs/fuse/inode.c | 6 +
include/uapi/linux/fuse.h | 1 +
4 files changed, 413 insertions(+)

diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index b52f9baaa3e7..449a6b315327 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -18,9 +18,16 @@
#include <linux/swap.h>
#include <linux/falloc.h>
#include <linux/uio.h>
+#include <linux/dax.h>
+#include <linux/iomap.h>
+#include <linux/interval_tree_generic.h>

static const struct file_operations fuse_direct_io_file_operations;

+INTERVAL_TREE_DEFINE(struct fuse_dax_mapping,
+ rb, __u64, __subtree_last,
+ START, LAST, static inline, fuse_dax_interval_tree);
+
static int fuse_send_open(struct fuse_conn *fc, u64 nodeid, struct file *file,
int opcode, struct fuse_open_out *outargp)
{
@@ -172,6 +179,171 @@ static void fuse_link_write_file(struct file *file)
spin_unlock(&fc->lock);
}

+static struct fuse_dax_mapping *alloc_dax_mapping(struct fuse_conn *fc)
+{
+ struct fuse_dax_mapping *dmap = NULL;
+
+ spin_lock(&fc->lock);
+
+ /* TODO: Add logic to try to free up memory if wait is allowed */
+ if (fc->nr_free_ranges <= 0) {
+ spin_unlock(&fc->lock);
+ return NULL;
+ }
+
+ WARN_ON(list_empty(&fc->free_ranges));
+
+ /* Take a free range */
+ dmap = list_first_entry(&fc->free_ranges, struct fuse_dax_mapping,
+ list);
+ list_del_init(&dmap->list);
+ fc->nr_free_ranges--;
+ spin_unlock(&fc->lock);
+ return dmap;
+}
+
+/* This assumes fc->lock is held */
+static void __free_dax_mapping(struct fuse_conn *fc,
+ struct fuse_dax_mapping *dmap)
+{
+ list_add_tail(&dmap->list, &fc->free_ranges);
+ fc->nr_free_ranges++;
+}
+
+static void free_dax_mapping(struct fuse_conn *fc,
+ struct fuse_dax_mapping *dmap)
+{
+ /* Return fuse_dax_mapping to free list */
+ spin_lock(&fc->lock);
+ __free_dax_mapping(fc, dmap);
+ spin_unlock(&fc->lock);
+}
+
+/* offset passed in should be aligned to FUSE_DAX_MEM_RANGE_SZ */
+static int fuse_setup_one_mapping(struct inode *inode,
+ struct file *file, loff_t offset,
+ struct fuse_dax_mapping *dmap)
+{
+ struct fuse_conn *fc = get_fuse_conn(inode);
+ struct fuse_inode *fi = get_fuse_inode(inode);
+ struct fuse_file *ff = NULL;
+ struct fuse_setupmapping_in inarg;
+ FUSE_ARGS(args);
+ ssize_t err;
+
+ if (file)
+ ff = file->private_data;
+
+ WARN_ON(offset % FUSE_DAX_MEM_RANGE_SZ);
+ WARN_ON(fc->nr_free_ranges < 0);
+
+ /* Ask fuse daemon to setup mapping */
+ memset(&inarg, 0, sizeof(inarg));
+ inarg.foffset = offset;
+ if (ff)
+ inarg.fh = ff->fh;
+ else
+ inarg.fh = -1;
+ inarg.moffset = dmap->window_offset;
+ inarg.len = FUSE_DAX_MEM_RANGE_SZ;
+ if (file) {
+ inarg.flags |= (file->f_mode & FMODE_WRITE) ?
+ FUSE_SETUPMAPPING_FLAG_WRITE : 0;
+ inarg.flags |= (file->f_mode & FMODE_READ) ?
+ FUSE_SETUPMAPPING_FLAG_READ : 0;
+ } else {
+ inarg.flags |= FUSE_SETUPMAPPING_FLAG_READ;
+ inarg.flags |= FUSE_SETUPMAPPING_FLAG_WRITE;
+ }
+ args.in.h.opcode = FUSE_SETUPMAPPING;
+ args.in.h.nodeid = fi->nodeid;
+ args.in.numargs = 1;
+ args.in.args[0].size = sizeof(inarg);
+ args.in.args[0].value = &inarg;
+ err = fuse_simple_request(fc, &args);
+ if (err < 0) {
+ printk(KERN_ERR "%s request failed at mem_offset=0x%llx %zd\n",
+ __func__, dmap->window_offset, err);
+ return err;
+ }
+
+ pr_debug("fuse_setup_one_mapping() succeeded. offset=0x%llx err=%zd\n", offset, err);
+
+ /* TODO: What locking is required here. For now, using fc->lock */
+ dmap->start = offset;
+ dmap->end = offset + FUSE_DAX_MEM_RANGE_SZ - 1;
+ /* Protected by fi->i_dmap_sem */
+ fuse_dax_interval_tree_insert(dmap, &fi->dmap_tree);
+ fi->nr_dmaps++;
+ return 0;
+}
+
+static int fuse_removemapping_one(struct inode *inode,
+ struct fuse_dax_mapping *dmap)
+{
+ struct fuse_inode *fi = get_fuse_inode(inode);
+ struct fuse_conn *fc = get_fuse_conn(inode);
+ struct fuse_removemapping_in inarg;
+ FUSE_ARGS(args);
+ ssize_t err = 0;
+
+ memset(&inarg, 0, sizeof(inarg));
+ inarg.moffset = dmap->window_offset;
+ inarg.len = dmap->length;
+ args.in.h.opcode = FUSE_REMOVEMAPPING;
+ args.in.h.nodeid = fi->nodeid;
+ args.in.numargs = 1;
+ args.in.args[0].size = sizeof(inarg);
+ args.in.args[0].value = &inarg;
+ err = fuse_simple_request(fc, &args);
+ if (err < 0) {
+ printk(KERN_ERR "%s request failed %zd\n", __func__, err);
+ return err;
+ }
+ pr_debug("%s request succeeded\n", __func__);
+ return 0;
+}
+
+void fuse_removemapping(struct inode *inode)
+{
+ struct fuse_conn *fc = get_fuse_conn(inode);
+ struct fuse_inode *fi = get_fuse_inode(inode);
+ ssize_t err;
+ struct fuse_dax_mapping *dmap;
+
+ down_write(&fi->i_dmap_sem);
+
+ /* Clear the mappings list */
+ while (true) {
+ WARN_ON(fi->nr_dmaps < 0);
+
+ dmap = fuse_dax_interval_tree_iter_first(&fi->dmap_tree, 0,
+ -1);
+ if (dmap) {
+ fuse_dax_interval_tree_remove(dmap, &fi->dmap_tree);
+ fi->nr_dmaps--;
+ }
+
+ if (!dmap)
+ break;
+
+ err = fuse_removemapping_one(inode, dmap);
+ if (err) {
+ /* TODO: Add it back to tree. */
+ printk("Failed to removemapping. offset=0x%llx"
+ " len=0x%llx\n", dmap->window_offset,
+ dmap->length);
+ continue;
+ }
+
+ /* Add it back to free ranges list */
+ free_dax_mapping(fc, dmap);
+ }
+
+ up_write(&fi->i_dmap_sem);
+ pr_debug("%s request succeeded\n", __func__);
+}
+
void fuse_finish_open(struct inode *inode, struct file *file)
{
struct fuse_file *ff = file->private_data;
@@ -1452,6 +1624,204 @@ static ssize_t fuse_direct_write_iter(struct kiocb *iocb, struct iov_iter *from)
return res;
}

+static void fuse_fill_iomap_hole(struct iomap *iomap, loff_t length)
+{
+ iomap->addr = IOMAP_NULL_ADDR;
+ iomap->length = length;
+ iomap->type = IOMAP_HOLE;
+}
+
+static void fuse_fill_iomap(struct inode *inode, loff_t pos, loff_t length,
+ struct iomap *iomap, struct fuse_dax_mapping *dmap,
+ unsigned flags)
+{
+ loff_t offset, len;
+ loff_t i_size = i_size_read(inode);
+
+ offset = pos - dmap->start;
+ len = min(length, dmap->length - offset);
+
+ /* If length is beyond end of file, truncate further */
+ if (pos + len > i_size)
+ len = i_size - pos;
+
+ if (len > 0) {
+ iomap->addr = dmap->window_offset + offset;
+ iomap->length = len;
+ if (flags & IOMAP_FAULT)
+ iomap->length = ALIGN(len, PAGE_SIZE);
+ iomap->type = IOMAP_MAPPED;
+ pr_debug("%s: returns iomap: addr 0x%llx offset 0x%llx"
+ " length 0x%llx\n", __func__, iomap->addr,
+ iomap->offset, iomap->length);
+ } else {
+ /* Mapping beyond end of file is hole */
+ fuse_fill_iomap_hole(iomap, length);
+ pr_debug("%s: returns iomap: addr 0x%llx offset 0x%llx"
+ "length 0x%llx\n", __func__, iomap->addr,
+ iomap->offset, iomap->length);
+ }
+}
+
+/* This is just for DAX and the mapping is ephemeral, do not use it for other
+ * purposes since there is no block device with a permanent mapping.
+ */
+static int fuse_iomap_begin(struct inode *inode, loff_t pos, loff_t length,
+ unsigned flags, struct iomap *iomap)
+{
+ struct fuse_inode *fi = get_fuse_inode(inode);
+ struct fuse_conn *fc = get_fuse_conn(inode);
+ struct fuse_dax_mapping *dmap, *alloc_dmap = NULL;
+ int ret;
+
+ /* We don't support FIEMAP */
+ BUG_ON(flags & IOMAP_REPORT);
+
+ pr_debug("fuse_iomap_begin() called. pos=0x%llx length=0x%llx\n",
+ pos, length);
+
+ iomap->offset = pos;
+ iomap->flags = 0;
+ iomap->bdev = NULL;
+ iomap->dax_dev = fc->dax_dev;
+
+ /*
+ * Both read/write and mmap path can race here. So we need something
+ * to make sure if we are setting up mapping, then other path waits
+ *
+ * For now, use a semaphore for this. It probably needs to be
+ * optimized later.
+ */
+ down_read(&fi->i_dmap_sem);
+ dmap = fuse_dax_interval_tree_iter_first(&fi->dmap_tree, pos, pos);
+
+ if (dmap) {
+ fuse_fill_iomap(inode, pos, length, iomap, dmap, flags);
+ up_read(&fi->i_dmap_sem);
+ return 0;
+ } else {
+ up_read(&fi->i_dmap_sem);
+ pr_debug("%s: no mapping at offset 0x%llx length 0x%llx\n",
+ __func__, pos, length);
+ if (pos >= i_size_read(inode))
+ goto iomap_hole;
+
+ alloc_dmap = alloc_dax_mapping(fc);
+ if (!alloc_dmap)
+ return -EBUSY;
+
+ /*
+ * Drop read lock and take write lock so that only one
+ * caller can try to setup mapping and other waits
+ */
+ down_write(&fi->i_dmap_sem);
+ /*
+ * We dropped lock. Check again if somebody else setup
+ * mapping already.
+ */
+ dmap = fuse_dax_interval_tree_iter_first(&fi->dmap_tree, pos,
+ pos);
+ if (dmap) {
+ fuse_fill_iomap(inode, pos, length, iomap, dmap, flags);
+ free_dax_mapping(fc, alloc_dmap);
+ up_write(&fi->i_dmap_sem);
+ return 0;
+ }
+
+ /* Setup one mapping */
+ ret = fuse_setup_one_mapping(inode, NULL,
+ ALIGN_DOWN(pos, FUSE_DAX_MEM_RANGE_SZ),
+ alloc_dmap);
+ if (ret < 0) {
+ printk("fuse_setup_one_mapping() failed. err=%d"
+ " pos=0x%llx\n", ret, pos);
+ free_dax_mapping(fc, alloc_dmap);
+ up_write(&fi->i_dmap_sem);
+ return ret;
+ }
+ fuse_fill_iomap(inode, pos, length, iomap, alloc_dmap, flags);
+ up_write(&fi->i_dmap_sem);
+ return 0;
+ }
+
+ /*
+ * If read beyond end of file happnes, fs code seems to return
+ * it as hole
+ */
+iomap_hole:
+ fuse_fill_iomap_hole(iomap, length);
+ pr_debug("fuse_iomap_begin() returning hole mapping. pos=0x%llx length_asked=0x%llx length_returned=0x%llx\n", pos, length, iomap->length);
+ return 0;
+}
+
+static int fuse_iomap_end(struct inode *inode, loff_t pos, loff_t length,
+ ssize_t written, unsigned flags,
+ struct iomap *iomap)
+{
+ /* DAX writes beyond end-of-file aren't handled using iomap, so the
+ * file size is unchanged and there is nothing to do here.
+ */
+ return 0;
+}
+
+static const struct iomap_ops fuse_iomap_ops = {
+ .iomap_begin = fuse_iomap_begin,
+ .iomap_end = fuse_iomap_end,
+};
+
+static ssize_t fuse_dax_read_iter(struct kiocb *iocb, struct iov_iter *to)
+{
+ struct inode *inode = file_inode(iocb->ki_filp);
+ ssize_t ret;
+
+ if (iocb->ki_flags & IOCB_NOWAIT) {
+ if (!inode_trylock_shared(inode))
+ return -EAGAIN;
+ } else {
+ inode_lock_shared(inode);
+ }
+
+ ret = dax_iomap_rw(iocb, to, &fuse_iomap_ops);
+ inode_unlock_shared(inode);
+
+ /* TODO file_accessed(iocb->f_filp) */
+
+ return ret;
+}
+
+static ssize_t fuse_dax_write_iter(struct kiocb *iocb, struct iov_iter *from)
+{
+ struct inode *inode = file_inode(iocb->ki_filp);
+ ssize_t ret;
+
+ if (iocb->ki_flags & IOCB_NOWAIT) {
+ if (!inode_trylock(inode))
+ return -EAGAIN;
+ } else {
+ inode_lock(inode);
+ }
+
+ ret = generic_write_checks(iocb, from);
+ if (ret <= 0)
+ goto out;
+
+ ret = file_remove_privs(iocb->ki_filp);
+ if (ret)
+ goto out;
+ /* TODO file_update_time() but we don't want metadata I/O */
+
+ /* TODO handle growing the file */
+
+ ret = dax_iomap_rw(iocb, from, &fuse_iomap_ops);
+
+out:
+ inode_unlock(inode);
+
+ if (ret > 0)
+ ret = generic_write_sync(iocb, ret);
+ return ret;
+}
+
static void fuse_writepage_free(struct fuse_conn *fc, struct fuse_req *req)
{
int i;
@@ -2104,6 +2474,11 @@ static int fuse_direct_mmap(struct file *file, struct vm_area_struct *vma)
return generic_file_mmap(file, vma);
}

+static int fuse_dax_mmap(struct file *file, struct vm_area_struct *vma)
+{
+ return -EINVAL; /* TODO */
+}
+
static int convert_fuse_file_lock(struct fuse_conn *fc,
const struct fuse_file_lock *ffl,
struct file_lock *fl)
@@ -3137,6 +3512,24 @@ static const struct file_operations fuse_direct_io_file_operations = {
/* no splice_read */
};

+static const struct file_operations fuse_dax_file_operations = {
+ .llseek = fuse_file_llseek,
+ .read_iter = fuse_dax_read_iter,
+ .write_iter = fuse_dax_write_iter,
+ .mmap = fuse_dax_mmap,
+ .open = fuse_open,
+ .flush = fuse_flush,
+ .release = fuse_release,
+ .fsync = fuse_fsync,
+ .lock = fuse_file_lock,
+ .flock = fuse_file_flock,
+ .unlocked_ioctl = fuse_file_ioctl,
+ .compat_ioctl = fuse_file_compat_ioctl,
+ .poll = fuse_file_poll,
+ .fallocate = fuse_file_fallocate,
+ /* no splice_read */
+};
+
static const struct address_space_operations fuse_file_aops = {
.readpage = fuse_readpage,
.writepage = fuse_writepage,
@@ -3153,6 +3546,7 @@ static const struct address_space_operations fuse_file_aops = {
void fuse_init_file_inode(struct inode *inode)
{
struct fuse_inode *fi = get_fuse_inode(inode);
+ struct fuse_conn *fc = get_fuse_conn(inode);

inode->i_fop = &fuse_file_operations;
inode->i_data.a_ops = &fuse_file_aops;
@@ -3162,4 +3556,10 @@ void fuse_init_file_inode(struct inode *inode)
fi->writectr = 0;
init_waitqueue_head(&fi->page_waitq);
INIT_LIST_HEAD(&fi->writepages);
+ fi->dmap_tree = RB_ROOT_CACHED;
+
+ if (fc->dax_dev) {
+ inode->i_flags |= S_DAX;
+ inode->i_fop = &fuse_dax_file_operations;
+ }
}
diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index a24f31156b47..3b17fb336256 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -203,6 +203,11 @@ struct fuse_inode {
/** Lock for serializing lookup and readdir for back compatibility*/
struct mutex mutex;

+ /*
+ * Semaphore to protect modifications to dmap_tree
+ */
+ struct rw_semaphore i_dmap_sem;
+
/** Sorted rb tree of struct fuse_dax_mapping elements */
struct rb_root_cached dmap_tree;
unsigned long nr_dmaps;
@@ -1225,5 +1230,6 @@ unsigned fuse_len_args(unsigned numargs, struct fuse_arg *args);
* Get the next unique ID for a request
*/
u64 fuse_get_unique(struct fuse_iqueue *fiq);
+void fuse_removemapping(struct inode *inode);

#endif /* _FS_FUSE_I_H */
diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
index 075997977cfd..56310d10cd4c 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -83,7 +83,9 @@ static struct inode *fuse_alloc_inode(struct super_block *sb)
fi->attr_version = 0;
fi->orig_ino = 0;
fi->state = 0;
+ fi->nr_dmaps = 0;
mutex_init(&fi->mutex);
+ init_rwsem(&fi->i_dmap_sem);
fi->forget = fuse_alloc_forget();
if (!fi->forget) {
kmem_cache_free(fuse_inode_cachep, inode);
@@ -118,6 +120,10 @@ static void fuse_evict_inode(struct inode *inode)
if (inode->i_sb->s_flags & SB_ACTIVE) {
struct fuse_conn *fc = get_fuse_conn(inode);
struct fuse_inode *fi = get_fuse_inode(inode);
+ if (IS_DAX(inode)) {
+ fuse_removemapping(inode);
+ WARN_ON(fi->nr_dmaps);
+ }
fuse_queue_forget(fc, fi->forget, fi->nodeid, fi->nlookup);
fi->forget = NULL;
}
diff --git a/include/uapi/linux/fuse.h b/include/uapi/linux/fuse.h
index 867fdafc4a5e..1657253cb7d6 100644
--- a/include/uapi/linux/fuse.h
+++ b/include/uapi/linux/fuse.h
@@ -821,6 +821,7 @@ struct fuse_copy_file_range_in {

#define FUSE_SETUPMAPPING_ENTRIES 8
#define FUSE_SETUPMAPPING_FLAG_WRITE (1ull << 0)
+#define FUSE_SETUPMAPPING_FLAG_READ (1ull << 1)
struct fuse_setupmapping_in {
/* An already open handle */
uint64_t fh;
--
2.13.6

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