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Subject[PATCH 13/14] fuse: Turn writeback cache on
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Introduce a bit kernel and userspace exchange between each-other on
the init stage and turn writeback on if the userspace want this and
mount option 'allow_wbcache' is present (controlled by fusermount).

Also add each writable file into per-inode write list and call the
generic_file_aio_write to make use of the Linux page cache engine.

Original patch by: Pavel Emelyanov <xemul@openvz.org>
Signed-off-by: Maxim Patlasov <MPatlasov@parallels.com>
---
fs/fuse/file.c | 15 +++++++++++++++
fs/fuse/fuse_i.h | 4 ++++
fs/fuse/inode.c | 13 +++++++++++++
include/uapi/linux/fuse.h | 2 ++
4 files changed, 34 insertions(+), 0 deletions(-)

diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index e6e064c..147e618 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -211,6 +211,8 @@ void fuse_finish_open(struct inode *inode, struct file *file)
spin_unlock(&fc->lock);
fuse_invalidate_attr(inode);
}
+ if ((file->f_mode & FMODE_WRITE) && fc->writeback_cache)
+ fuse_link_write_file(file);
}

int fuse_open_common(struct inode *inode, struct file *file, bool isdir)
@@ -1096,6 +1098,19 @@ static ssize_t fuse_file_aio_write(struct kiocb *iocb, const struct iovec *iov,
struct iov_iter i;
loff_t endbyte = 0;

+ if (get_fuse_conn(inode)->writeback_cache) {
+ if (!(file->f_flags & O_DIRECT)) {
+ struct fuse_conn *fc = get_fuse_conn(inode);
+ struct fuse_inode *fi = get_fuse_inode(inode);
+
+ spin_lock(&fc->lock);
+ inode->i_mtime = current_fs_time(inode->i_sb);
+ set_bit(FUSE_I_MTIME_UPDATED, &fi->state);
+ spin_unlock(&fc->lock);
+ }
+ return generic_file_aio_write(iocb, iov, nr_segs, pos);
+ }
+
WARN_ON(iocb->ki_pos != pos);

ocount = 0;
diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index 86caa8c..a207744 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -44,6 +44,10 @@
doing the mount will be allowed to access the filesystem */
#define FUSE_ALLOW_OTHER (1 << 1)

+/** If the FUSE_ALLOW_WBCACHE flag is given, the filesystem
+ module will enable support of writback cache */
+#define FUSE_ALLOW_WBCACHE (1 << 2)
+
/** Number of page pointers embedded in fuse_req */
#define FUSE_REQ_INLINE_PAGES 1

diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
index 3687daf..541fc4f 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -521,6 +521,7 @@ enum {
OPT_ALLOW_OTHER,
OPT_MAX_READ,
OPT_BLKSIZE,
+ OPT_ALLOW_WBCACHE,
OPT_ERR
};

@@ -533,6 +534,7 @@ static const match_table_t tokens = {
{OPT_ALLOW_OTHER, "allow_other"},
{OPT_MAX_READ, "max_read=%u"},
{OPT_BLKSIZE, "blksize=%u"},
+ {OPT_ALLOW_WBCACHE, "allow_wbcache"},
{OPT_ERR, NULL}
};

@@ -606,6 +608,10 @@ static int parse_fuse_opt(char *opt, struct fuse_mount_data *d, int is_bdev)
d->blksize = value;
break;

+ case OPT_ALLOW_WBCACHE:
+ d->flags |= FUSE_ALLOW_WBCACHE;
+ break;
+
default:
return 0;
}
@@ -633,6 +639,8 @@ static int fuse_show_options(struct seq_file *m, struct dentry *root)
seq_printf(m, ",max_read=%u", fc->max_read);
if (sb->s_bdev && sb->s_blocksize != FUSE_DEFAULT_BLKSIZE)
seq_printf(m, ",blksize=%lu", sb->s_blocksize);
+ if (fc->flags & FUSE_ALLOW_WBCACHE)
+ seq_puts(m, ",allow_wbcache");
return 0;
}

@@ -944,6 +952,9 @@ static void process_init_reply(struct fuse_conn *fc, struct fuse_req *req)
fc->auto_inval_data = 1;
if (arg->flags & FUSE_DO_READDIRPLUS)
fc->do_readdirplus = 1;
+ if (arg->flags & FUSE_WRITEBACK_CACHE &&
+ fc->flags & FUSE_ALLOW_WBCACHE)
+ fc->writeback_cache = 1;
} else {
ra_pages = fc->max_read / PAGE_CACHE_SIZE;
fc->no_lock = 1;
@@ -972,6 +983,8 @@ static void fuse_send_init(struct fuse_conn *fc, struct fuse_req *req)
FUSE_SPLICE_WRITE | FUSE_SPLICE_MOVE | FUSE_SPLICE_READ |
FUSE_FLOCK_LOCKS | FUSE_IOCTL_DIR | FUSE_AUTO_INVAL_DATA |
FUSE_DO_READDIRPLUS;
+ if (fc->flags & FUSE_ALLOW_WBCACHE)
+ arg->flags |= FUSE_WRITEBACK_CACHE;
req->in.h.opcode = FUSE_INIT;
req->in.numargs = 1;
req->in.args[0].size = sizeof(*arg);
diff --git a/include/uapi/linux/fuse.h b/include/uapi/linux/fuse.h
index 5dc1fea..20a9553 100644
--- a/include/uapi/linux/fuse.h
+++ b/include/uapi/linux/fuse.h
@@ -179,6 +179,7 @@ struct fuse_file_lock {
* FUSE_FLOCK_LOCKS: remote locking for BSD style file locks
* FUSE_HAS_IOCTL_DIR: kernel supports ioctl on directories
* FUSE_AUTO_INVAL_DATA: automatically invalidate cached pages
+ * FUSE_WRITEBACK_CACHE: use writeback cache for buffered writes
*/
#define FUSE_ASYNC_READ (1 << 0)
#define FUSE_POSIX_LOCKS (1 << 1)
@@ -194,6 +195,7 @@ struct fuse_file_lock {
#define FUSE_HAS_IOCTL_DIR (1 << 11)
#define FUSE_AUTO_INVAL_DATA (1 << 12)
#define FUSE_DO_READDIRPLUS (1 << 13)
+#define FUSE_WRITEBACK_CACHE (1 << 14)

/**
* CUSE INIT request/reply flags


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