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Subject[PATCH 06/14] fuse: Trust kernel i_size only - v2
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Make fuse think that when writeback is on the inode's i_size is always
up-to-date and not update it with the value received from the userspace.
This is done because the page cache code may update i_size without letting
the FS know.

This assumption implies fixing the previously introduced short-read helper --
when a short read occurs the 'hole' is filled with zeroes.

fuse_file_fallocate() is also fixed because now we should keep i_size up to
date, so it must be updated if FUSE_FALLOCATE request succeeded.

Changed in v2:
- improved comment in fuse_short_read()
- fixed fuse_file_fallocate() for KEEP_SIZE mode

Original patch by: Pavel Emelyanov <xemul@openvz.org>
Signed-off-by: Maxim V. Patlasov <MPatlasov@parallels.com>
---
fs/fuse/dir.c | 9 ++++++---
fs/fuse/file.c | 43 +++++++++++++++++++++++++++++++++++++++++--
fs/fuse/inode.c | 6 ++++--
3 files changed, 51 insertions(+), 7 deletions(-)

diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
index ed8f8c5..ff8b603 100644
--- a/fs/fuse/dir.c
+++ b/fs/fuse/dir.c
@@ -827,7 +827,7 @@ static void fuse_fillattr(struct inode *inode, struct fuse_attr *attr,
stat->mtime.tv_nsec = attr->mtimensec;
stat->ctime.tv_sec = attr->ctime;
stat->ctime.tv_nsec = attr->ctimensec;
- stat->size = attr->size;
+ stat->size = i_size_read(inode);
stat->blocks = attr->blocks;

if (attr->blksize != 0)
@@ -1541,6 +1541,7 @@ static int fuse_do_setattr(struct dentry *entry, struct iattr *attr,
struct fuse_setattr_in inarg;
struct fuse_attr_out outarg;
bool is_truncate = false;
+ bool is_wb = fc->writeback_cache;
loff_t oldsize;
int err;

@@ -1613,7 +1614,8 @@ static int fuse_do_setattr(struct dentry *entry, struct iattr *attr,
fuse_change_attributes_common(inode, &outarg.attr,
attr_timeout(&outarg));
oldsize = inode->i_size;
- i_size_write(inode, outarg.attr.size);
+ if (!is_wb || is_truncate || !S_ISREG(inode->i_mode))
+ i_size_write(inode, outarg.attr.size);

if (is_truncate) {
/* NOTE: this may release/reacquire fc->lock */
@@ -1625,7 +1627,8 @@ static int fuse_do_setattr(struct dentry *entry, struct iattr *attr,
* Only call invalidate_inode_pages2() after removing
* FUSE_NOWRITE, otherwise fuse_launder_page() would deadlock.
*/
- if (S_ISREG(inode->i_mode) && oldsize != outarg.attr.size) {
+ if ((is_truncate || !is_wb) &&
+ S_ISREG(inode->i_mode) && oldsize != outarg.attr.size) {
truncate_pagecache(inode, oldsize, outarg.attr.size);
invalidate_inode_pages2(inode->i_mapping);
}
diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index b28be33..6b64e11 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -15,6 +15,7 @@
#include <linux/module.h>
#include <linux/compat.h>
#include <linux/swap.h>
+#include <linux/falloc.h>

static const struct file_operations fuse_direct_io_file_operations;

@@ -543,9 +544,31 @@ static void fuse_short_read(struct fuse_req *req, struct inode *inode,
u64 attr_ver)
{
size_t num_read = req->out.args[0].size;
+ struct fuse_conn *fc = get_fuse_conn(inode);
+
+ if (fc->writeback_cache) {
+ /*
+ * A hole in a file. Some data after the hole are in page cache,
+ * but have not reached the client fs yet. So, the hole is not
+ * present there.
+ */
+ int i;
+ int start_idx = num_read >> PAGE_CACHE_SHIFT;
+ size_t off = num_read & (PAGE_CACHE_SIZE - 1);

- loff_t pos = page_offset(req->pages[0]) + num_read;
- fuse_read_update_size(inode, pos, attr_ver);
+ for (i = start_idx; i < req->num_pages; i++) {
+ struct page *page = req->pages[i];
+ void *mapaddr = kmap_atomic(page);
+
+ memset(mapaddr + off, 0, PAGE_CACHE_SIZE - off);
+
+ kunmap_atomic(mapaddr);
+ off = 0;
+ }
+ } else {
+ loff_t pos = page_offset(req->pages[0]) + num_read;
+ fuse_read_update_size(inode, pos, attr_ver);
+ }
}

static int fuse_readpage(struct file *file, struct page *page)
@@ -2285,6 +2308,8 @@ static long fuse_file_fallocate(struct file *file, int mode, loff_t offset,
.mode = mode
};
int err;
+ bool change_i_size = fc->writeback_cache &&
+ !(mode & FALLOC_FL_KEEP_SIZE);

if (fc->no_fallocate)
return -EOPNOTSUPP;
@@ -2293,6 +2318,11 @@ static long fuse_file_fallocate(struct file *file, int mode, loff_t offset,
if (IS_ERR(req))
return PTR_ERR(req);

+ if (change_i_size) {
+ struct inode *inode = file->f_mapping->host;
+ mutex_lock(&inode->i_mutex);
+ }
+
req->in.h.opcode = FUSE_FALLOCATE;
req->in.h.nodeid = ff->nodeid;
req->in.numargs = 1;
@@ -2306,6 +2336,15 @@ static long fuse_file_fallocate(struct file *file, int mode, loff_t offset,
}
fuse_put_request(fc, req);

+ if (change_i_size) {
+ struct inode *inode = file->f_mapping->host;
+
+ if (!err)
+ fuse_write_update_size(inode, offset + length);
+
+ mutex_unlock(&inode->i_mutex);
+ }
+
return err;
}

diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
index 9d95a5a..7e07dbd 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -196,6 +196,7 @@ void fuse_change_attributes(struct inode *inode, struct fuse_attr *attr,
{
struct fuse_conn *fc = get_fuse_conn(inode);
struct fuse_inode *fi = get_fuse_inode(inode);
+ bool is_wb = fc->writeback_cache;
loff_t oldsize;
struct timespec old_mtime;

@@ -209,10 +210,11 @@ void fuse_change_attributes(struct inode *inode, struct fuse_attr *attr,
fuse_change_attributes_common(inode, attr, attr_valid);

oldsize = inode->i_size;
- i_size_write(inode, attr->size);
+ if (!is_wb || !S_ISREG(inode->i_mode))
+ i_size_write(inode, attr->size);
spin_unlock(&fc->lock);

- if (S_ISREG(inode->i_mode)) {
+ if (!is_wb && S_ISREG(inode->i_mode)) {
bool inval = false;

if (oldsize != attr->size) {


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