ce8d2cdf3d
Why do we need r/o bind mounts? This feature allows a read-only view into a read-write filesystem. In the process of doing that, it also provides infrastructure for keeping track of the number of writers to any given mount. This has a number of uses. It allows chroots to have parts of filesystems writable. It will be useful for containers in the future because users may have root inside a container, but should not be allowed to write to somefilesystems. This also replaces patches that vserver has had out of the tree for several years. It allows security enhancement by making sure that parts of your filesystem read-only (such as when you don't trust your FTP server), when you don't want to have entire new filesystems mounted, or when you want atime selectively updated. I've been using the following script to test that the feature is working as desired. It takes a directory and makes a regular bind and a r/o bind mount of it. It then performs some normal filesystem operations on the three directories, including ones that are expected to fail, like creating a file on the r/o mount. This patch: Some filesystems forego the vfs and may_open() and create their own 'struct file's. This patch creates a couple of helper functions which can be used by these filesystems, and will provide a unified place which the r/o bind mount code may patch. Also, rename an existing, static-scope init_file() to a less generic name. Signed-off-by: Dave Hansen <haveblue@us.ibm.com> Cc: Christoph Hellwig <hch@lst.de> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
123 lines
3.1 KiB
C
123 lines
3.1 KiB
C
/*
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* Wrapper functions for accessing the file_struct fd array.
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*/
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#ifndef __LINUX_FILE_H
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#define __LINUX_FILE_H
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#include <asm/atomic.h>
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#include <linux/posix_types.h>
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#include <linux/compiler.h>
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#include <linux/spinlock.h>
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#include <linux/rcupdate.h>
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#include <linux/types.h>
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/*
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* The default fd array needs to be at least BITS_PER_LONG,
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* as this is the granularity returned by copy_fdset().
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*/
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#define NR_OPEN_DEFAULT BITS_PER_LONG
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/*
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* The embedded_fd_set is a small fd_set,
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* suitable for most tasks (which open <= BITS_PER_LONG files)
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*/
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struct embedded_fd_set {
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unsigned long fds_bits[1];
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};
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struct fdtable {
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unsigned int max_fds;
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struct file ** fd; /* current fd array */
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fd_set *close_on_exec;
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fd_set *open_fds;
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struct rcu_head rcu;
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struct fdtable *next;
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};
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/*
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* Open file table structure
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*/
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struct files_struct {
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/*
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* read mostly part
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*/
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atomic_t count;
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struct fdtable *fdt;
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struct fdtable fdtab;
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/*
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* written part on a separate cache line in SMP
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*/
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spinlock_t file_lock ____cacheline_aligned_in_smp;
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int next_fd;
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struct embedded_fd_set close_on_exec_init;
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struct embedded_fd_set open_fds_init;
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struct file * fd_array[NR_OPEN_DEFAULT];
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};
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#define files_fdtable(files) (rcu_dereference((files)->fdt))
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extern struct kmem_cache *filp_cachep;
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extern void FASTCALL(__fput(struct file *));
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extern void FASTCALL(fput(struct file *));
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struct file_operations;
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struct vfsmount;
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struct dentry;
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extern int init_file(struct file *, struct vfsmount *mnt,
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struct dentry *dentry, mode_t mode,
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const struct file_operations *fop);
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extern struct file *alloc_file(struct vfsmount *, struct dentry *dentry,
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mode_t mode, const struct file_operations *fop);
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static inline void fput_light(struct file *file, int fput_needed)
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{
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if (unlikely(fput_needed))
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fput(file);
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}
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extern struct file * FASTCALL(fget(unsigned int fd));
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extern struct file * FASTCALL(fget_light(unsigned int fd, int *fput_needed));
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extern void FASTCALL(set_close_on_exec(unsigned int fd, int flag));
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extern void put_filp(struct file *);
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extern int get_unused_fd(void);
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extern int get_unused_fd_flags(int flags);
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extern void FASTCALL(put_unused_fd(unsigned int fd));
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struct kmem_cache;
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extern int expand_files(struct files_struct *, int nr);
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extern void free_fdtable_rcu(struct rcu_head *rcu);
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extern void __init files_defer_init(void);
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static inline void free_fdtable(struct fdtable *fdt)
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{
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call_rcu(&fdt->rcu, free_fdtable_rcu);
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}
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static inline struct file * fcheck_files(struct files_struct *files, unsigned int fd)
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{
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struct file * file = NULL;
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struct fdtable *fdt = files_fdtable(files);
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if (fd < fdt->max_fds)
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file = rcu_dereference(fdt->fd[fd]);
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return file;
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}
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/*
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* Check whether the specified fd has an open file.
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*/
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#define fcheck(fd) fcheck_files(current->files, fd)
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extern void FASTCALL(fd_install(unsigned int fd, struct file * file));
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struct task_struct;
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struct files_struct *get_files_struct(struct task_struct *);
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void FASTCALL(put_files_struct(struct files_struct *fs));
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void reset_files_struct(struct task_struct *, struct files_struct *);
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extern struct kmem_cache *files_cachep;
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#endif /* __LINUX_FILE_H */
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