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SubjectRe: [RFC PATCH 4/4] Directory listing support for union mounted directories.
On Wed, Jun 20, 2007 at 11:24:18AM +0530, Bharata B Rao wrote:
> From: Bharata B Rao <bharata@linux.vnet.ibm.com>
> Subject: Directory listing support for union mounted directories.
>
> Modifies readdir()/getdents() to support union mounted directories.
>
> This patch adds support to readdir()/getdents() to read directory entries
> from all the directories of the union stack, and present a merged view to
> the userspace. This is achieved by maintaining a cache of read entries.
>
> TODO: Breaks lseek on union mounted directories, Fix this.

Btw, to avoid dealing with file structs representing multiple objects
->readdir should be changed to an inode_operation and not take a struct
file * but rather struct inode + loff_t *ppos. This sounds like a nice
preparatory patch for any kind of union mount implementation and is
acceptable standing on it's own.

>
> Signed-off-by: Bharata B Rao <bharata@linux.vnet.ibm.com>
> ---
> fs/file_table.c | 1
> fs/readdir.c | 242 ++++++++++++++++++++++++++++++++++++++++++++++++++++-
> include/linux/fs.h | 12 ++
> 3 files changed, 254 insertions(+), 1 deletion(-)
>
> --- a/fs/file_table.c
> +++ b/fs/file_table.c
> @@ -174,6 +174,7 @@ void fastcall __fput(struct file *file)
> if (file->f_mode & FMODE_WRITE)
> put_write_access(inode);
> put_pid(file->f_owner.pid);
> + put_rdstate(file->f_rdstate);
> file_kill(file);
> file->f_path.dentry = NULL;
> file->f_path.mnt = NULL;
> --- a/fs/readdir.c
> +++ b/fs/readdir.c
> @@ -19,6 +19,8 @@
>
> #include <asm/uaccess.h>
>
> +int readdir_union(struct file *file, void *buf, filldir_t filler);
> +
> int vfs_readdir(struct file *file, filldir_t filler, void *buf)
> {
> struct inode *inode = file->f_path.dentry->d_inode;
> @@ -33,7 +35,10 @@ int vfs_readdir(struct file *file, filld
> mutex_lock(&inode->i_mutex);
> res = -ENOENT;
> if (!IS_DEADDIR(inode)) {
> - res = file->f_op->readdir(file, buf, filler);
> + if (IS_MNT_UNION(file->f_path.mnt))
> + res = readdir_union(file, buf, filler);
> + else
> + res = file->f_op->readdir(file, buf, filler);
> file_accessed(file);
> }
> mutex_unlock(&inode->i_mutex);
> @@ -303,3 +308,238 @@ out_putf:
> out:
> return error;
> }
> +
> +/*
> + * NOTE: Some of the code below which maintains a list of dirents as a cache
> + * is from Jan Blunck's original union mount readdir patch.
> + */
> +
> +/* The readdir cache object */
> +struct rdcache_entry {
> + struct list_head list;
> + struct qstr name;
> +};
> +
> +struct rdcache_callback {
> + void *buf; /* original callback buffer */
> + filldir_t filldir; /* the filldir() we should call */
> + int error; /* stores filldir error */
> + struct rdstate *rdstate; /* readdir state */
> +};
> +
> +static int rdcache_add_entry(struct list_head *list,
> + const char *name, int namelen)
> +{
> + struct rdcache_entry *this;
> + char *tmp_name;
> +
> + this = kmalloc(sizeof(*this), GFP_KERNEL);
> + if (!this) {
> + printk(KERN_CRIT "rdcache_add_entry(): out of kernel memory\n");
> + return -ENOMEM;
> + }
> +
> + tmp_name = kmalloc(namelen + 1, GFP_KERNEL);
> + if (!tmp_name) {
> + printk(KERN_CRIT "rdcache_add_entry(): out of kernel memory\n");
> + kfree(this);
> + return -ENOMEM;
> + }
> +
> + this->name.name = tmp_name;
> + this->name.len = namelen;
> + this->name.hash = 0;
> + memcpy(tmp_name, name, namelen);
> + tmp_name[namelen] = 0;
> + INIT_LIST_HEAD(&this->list);
> + list_add(&this->list, list);
> + return 0;
> +}
> +
> +static void rdcache_free(struct list_head *list)
> +{
> + struct list_head *p;
> + struct list_head *ptmp;
> + int count = 0;
> +
> + list_for_each_safe(p, ptmp, list) {
> + struct rdcache_entry *this;
> +
> + this = list_entry(p, struct rdcache_entry, list);
> + list_del_init(&this->list);
> + kfree(this->name.name);
> + kfree(this);
> + count++;
> + }
> + return;
> +}
> +
> +static int rdcache_find_entry(struct list_head *uc_list,
> + const char *name, int namelen)
> +{
> + struct rdcache_entry *p;
> + int ret = 0;
> +
> + list_for_each_entry(p, uc_list, list) {
> + if (p->name.len != namelen)
> + continue;
> + if (strncmp(p->name.name, name, namelen) == 0) {
> + ret = 1;
> + break;
> + }
> + }
> + return ret;
> +}
> +
> +/*
> + * filldir routine for union mounted directories.
> + * Handles duplicate elimination by building a readdir cache.
> + * TODO: readdir cache is a linked list. Check if this can be designed
> + * more efficiently.
> + */
> +static int filldir_union(void *buf, const char *name, int namlen,
> + loff_t offset, u64 ino, unsigned int d_type)
> +{
> + struct rdcache_callback *cb = buf;
> + int err;
> +
> + if (rdcache_find_entry(&cb->rdstate->dirent_cache, name, namlen))
> + return 0;
> +
> + err = cb->filldir(cb->buf, name, namlen, offset, ino, d_type);
> + if (err >= 0)
> + rdcache_add_entry(&cb->rdstate->dirent_cache, name, namlen);
> + cb->error = err;
> + return err;
> +}
> +
> +/* Called from last fput() */
> +void put_rdstate(struct rdstate *rdstate)
> +{
> + if (!rdstate)
> + return;
> +
> + mntput(rdstate->mnt);
> + dput(rdstate->dentry);
> + rdcache_free(&rdstate->dirent_cache);
> + kfree(rdstate);
> +}
> +
> +static struct rdstate *get_rdstate(struct file *file)
> +{
> + if (file->f_rdstate)
> + return file->f_rdstate;
> +
> + /*
> + * We have read the dirents from this earlier but now don't have a
> + * corresponding rdstate. This shouldn't happen.
> + */
> + if (file->f_pos)
> + return ERR_PTR(-EINVAL);
> +
> + file->f_rdstate = kmalloc(sizeof(struct rdstate), GFP_KERNEL);
> + if (!file->f_rdstate)
> + return ERR_PTR(-ENOMEM);
> +
> + file->f_rdstate->off = 0;
> + file->f_rdstate->mnt = mntget(file->f_path.mnt);
> + file->f_rdstate->dentry = dget(file->f_path.dentry);
> + INIT_LIST_HEAD(&file->f_rdstate->dirent_cache);
> + return file->f_rdstate;
> +}
> +
> +int readdir_union(struct file *file, void *buf, filldir_t filler)
> +{
> + struct dentry *topmost = file->f_path.dentry;
> + struct rdstate *rdstate;
> + struct nameidata nd;
> + loff_t offset = 0;
> + struct rdcache_callback cb;
> + int err = 0;
> +
> + /*
> + * If this is not a union mount point or not a unioned directory
> + * within the union mount point, do readdir in the normal way.
> + */
> + nd.mnt = file->f_path.mnt;
> + nd.dentry = file->f_path.dentry;
> + if (!next_union_mount_exists(nd.mnt, nd.dentry))
> + return file->f_op->readdir(file, buf, filler);
> +
> + rdstate = get_rdstate(file);
> + if (IS_ERR(rdstate)) {
> + err = PTR_ERR(rdstate);
> + return err;
> + }
> +
> + cb.buf = buf;
> + cb.filldir = filler;
> + cb.rdstate = rdstate;
> +
> + offset = rdstate->off;
> +
> + /* Read from the topmost directory */
> + if (rdstate->dentry == topmost) {
> + file->f_pos = offset;
> + err = file->f_op->readdir(file, &cb, filldir_union);
> + rdstate->off = file->f_pos;
> + if (err < 0 || cb.error < 0)
> + goto out;
> +
> + /*
> + * Reading from topmost dir complete, start reading the lower
> + * dir from the beginning.
> + */
> + offset = 0;
> + } else {
> + nd.mnt = rdstate->mnt;
> + nd.dentry = rdstate->dentry;
> + goto read_lower;
> + }
> +
> + if (!next_union_mount(&nd))
> + return err;
> +
> +read_lower:
> + do {
> + struct vfsmount *mnt_tmp = mntget(nd.mnt);
> + struct dentry *dentry_tmp = dget(nd.dentry);
> + struct file *ftmp = dentry_open(nd.dentry, nd.mnt,
> + file->f_flags);
> + if (IS_ERR(ftmp)) {
> + mntput(mnt_tmp);
> + dput(dentry_tmp);
> + err = PTR_ERR(ftmp);
> + goto out;
> + }
> +
> + mutex_lock(&nd.dentry->d_inode->i_mutex);
> + ftmp->f_pos = offset;
> +
> + err = ftmp->f_op->readdir(ftmp, &cb, filldir_union);
> + file_accessed(ftmp);
> + rdstate->off = ftmp->f_pos;
> + mutex_unlock(&nd.dentry->d_inode->i_mutex);
> + if (nd.mnt != rdstate->mnt) {
> + mntput(rdstate->mnt);
> + rdstate->mnt = mntget(nd.mnt);
> + }
> + if (nd.dentry != rdstate->dentry) {
> + dput(rdstate->dentry);
> + rdstate->dentry = dget(nd.dentry);
> + }
> + fput(ftmp);
> + if (err < 0 || cb.error < 0)
> + goto out;
> +
> + /*
> + * Reading from a lower dir complete, start reading the
> + * next lower dir from the beginning.
> + */
> + offset = 0;
> + } while (next_union_mount(&nd));
> +
> + return 0;
> +out:
> + return err;
> +}
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -841,6 +841,14 @@ static inline void ra_set_size(struct fi
> unsigned long ra_submit(struct file_ra_state *ra,
> struct address_space *mapping, struct file *filp);
>
> +/* Direct cache for readdir, used for union mounted directories. */
> +struct rdstate {
> + struct vfsmount *mnt;
> + struct dentry *dentry;
> + loff_t off;
> + struct list_head dirent_cache;
> +};
> +
> struct file {
> /*
> * fu_list becomes invalid after file_free is called and queued via
> @@ -875,6 +883,7 @@ struct file {
> spinlock_t f_ep_lock;
> #endif /* #ifdef CONFIG_EPOLL */
> struct address_space *f_mapping;
> + struct rdstate *f_rdstate;
> };
> extern spinlock_t files_lock;
> #define file_list_lock() spin_lock(&files_lock);
> @@ -2119,5 +2128,8 @@ static inline void free_secdata(void *se
> { }
> #endif /* CONFIG_SECURITY */
>
> +/* fs/readdir.c */
> +void put_rdstate(struct rdstate *rdstate);
> +
> #endif /* __KERNEL__ */
> #endif /* _LINUX_FS_H */
> -
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