On Jun 27, 2023, at 10:06 AM, Bernd Schubert <bernd.schubert@xxxxxxxxxxx> wrote:
On 6/26/23 20:21, Chuck Lever wrote:
From: Chuck Lever <chuck.lever@xxxxxxxxxx>
The current cursor-based directory offset mechanism doesn't work
when a tmpfs filesystem is exported via NFS. This is because NFS
clients do not open directories. Each server-side READDIR operation
has to open the directory, read it, then close it. The cursor state
for that directory, being associated strictly with the opened
struct file, is thus discarded after each NFS READDIR operation.
Directory offsets are cached not only by NFS clients, but also by
user space libraries on those clients. Essentially there is no way
to invalidate those caches when directory offsets have changed on
an NFS server after the offset-to-dentry mapping changes. Thus the
whole application stack depends on unchanging directory offsets.
The solution we've come up with is to make the directory offset for
each file in a tmpfs filesystem stable for the life of the directory
entry it represents.
shmem_readdir() and shmem_dir_llseek() now use an xarray to map each
directory offset (an loff_t integer) to the memory address of a
struct dentry.
Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
---
mm/shmem.c | 54 +++++++++++++++++++++++++++++++++++++++++++++++-------
1 file changed, 47 insertions(+), 7 deletions(-)
diff --git a/mm/shmem.c b/mm/shmem.c
index 721f9fd064aa..89012f3583b1 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -2410,7 +2410,8 @@ static struct inode *shmem_get_inode(struct mnt_idmap *idmap, struct super_block
/* Some things misbehave if size == 0 on a directory */
inode->i_size = 2 * BOGO_DIRENT_SIZE;
inode->i_op = &shmem_dir_inode_operations;
- inode->i_fop = &simple_dir_operations;
+ inode->i_fop = &stable_dir_operations;
+ stable_offset_init(inode);
break;
case S_IFLNK:
/*
@@ -2950,7 +2951,10 @@ shmem_mknod(struct mnt_idmap *idmap, struct inode *dir,
if (error && error != -EOPNOTSUPP)
goto out_iput;
- error = 0;
+ error = stable_offset_add(dir, dentry);
+ if (error)
+ goto out_iput;
+
dir->i_size += BOGO_DIRENT_SIZE;
dir->i_ctime = dir->i_mtime = current_time(dir);
inode_inc_iversion(dir);
@@ -3027,6 +3031,13 @@ static int shmem_link(struct dentry *old_dentry, struct inode *dir, struct dentr
goto out;
}
+ ret = stable_offset_add(dir, dentry);
+ if (ret) {
+ if (inode->i_nlink)
+ shmem_free_inode(inode->i_sb);
+ goto out;
+ }
+
dir->i_size += BOGO_DIRENT_SIZE;
inode->i_ctime = dir->i_ctime = dir->i_mtime = current_time(inode);
inode_inc_iversion(dir);
@@ -3045,6 +3056,8 @@ static int shmem_unlink(struct inode *dir, struct dentry *dentry)
if (inode->i_nlink > 1 && !S_ISDIR(inode->i_mode))
shmem_free_inode(inode->i_sb);
+ stable_offset_remove(dir, dentry);
+
dir->i_size -= BOGO_DIRENT_SIZE;
inode->i_ctime = dir->i_ctime = dir->i_mtime = current_time(inode);
inode_inc_iversion(dir);
@@ -3103,24 +3116,41 @@ static int shmem_rename2(struct mnt_idmap *idmap,
{
struct inode *inode = d_inode(old_dentry);
int they_are_dirs = S_ISDIR(inode->i_mode);
+ int error;
if (flags & ~(RENAME_NOREPLACE | RENAME_EXCHANGE | RENAME_WHITEOUT))
return -EINVAL;
- if (flags & RENAME_EXCHANGE)
+ if (flags & RENAME_EXCHANGE) {
+ error = stable_offset_add(new_dir, old_dentry);
+ if (error)
+ return error;
Won't this fail in stable_offset_add() with -EBUSY, because dentry->d_offset is set?
+ error = stable_offset_add(old_dir, new_dentry);
+ if (error) {
+ stable_offset_remove(new_dir, old_dentry);
+ return error;
+ }
+ stable_offset_remove(old_dir, old_dentry);
+ stable_offset_remove(new_dir, new_dentry);
Assuming stable_offset_add() would have succeeded (somehow), old_dentry and new_dentry would have gotten reset their dentry->d_offset?
+
+ /* Always returns zero */
return simple_rename_exchange(old_dir, old_dentry, new_dir, new_dentry);
+ }
Hmm, let's assume simple_rename_exchange() fails, stable entries are now the other way around?
