![David Howells](/assets/img/avatar_default.png)
Extend the get_sb() filesystem operation to take an extra argument that permits the VFS to pass in the target vfsmount that defines the mountpoint. The filesystem is then required to manually set the superblock and root dentry pointers. For most filesystems, this should be done with simple_set_mnt() which will set the superblock pointer and then set the root dentry to the superblock's s_root (as per the old default behaviour). The get_sb() op now returns an integer as there's now no need to return the superblock pointer. This patch permits a superblock to be implicitly shared amongst several mount points, such as can be done with NFS to avoid potential inode aliasing. In such a case, simple_set_mnt() would not be called, and instead the mnt_root and mnt_sb would be set directly. The patch also makes the following changes: (*) the get_sb_*() convenience functions in the core kernel now take a vfsmount pointer argument and return an integer, so most filesystems have to change very little. (*) If one of the convenience function is not used, then get_sb() should normally call simple_set_mnt() to instantiate the vfsmount. This will always return 0, and so can be tail-called from get_sb(). (*) generic_shutdown_super() now calls shrink_dcache_sb() to clean up the dcache upon superblock destruction rather than shrink_dcache_anon(). This is required because the superblock may now have multiple trees that aren't actually bound to s_root, but that still need to be cleaned up. The currently called functions assume that the whole tree is rooted at s_root, and that anonymous dentries are not the roots of trees which results in dentries being left unculled. However, with the way NFS superblock sharing are currently set to be implemented, these assumptions are violated: the root of the filesystem is simply a dummy dentry and inode (the real inode for '/' may well be inaccessible), and all the vfsmounts are rooted on anonymous[*] dentries with child trees. [*] Anonymous until discovered from another tree. (*) The documentation has been adjusted, including the additional bit of changing ext2_* into foo_* in the documentation. [akpm@osdl.org: convert ipath_fs, do other stuff] Signed-off-by: David Howells <dhowells@redhat.com> Acked-by: Al Viro <viro@zeniv.linux.org.uk> Cc: Nathan Scott <nathans@sgi.com> Cc: Roland Dreier <rolandd@cisco.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
110 lines
2.4 KiB
C
110 lines
2.4 KiB
C
/*
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* mount.c - operations for initializing and mounting sysfs.
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*/
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#define DEBUG
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#include <linux/fs.h>
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#include <linux/mount.h>
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#include <linux/pagemap.h>
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#include <linux/init.h>
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#include "sysfs.h"
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/* Random magic number */
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#define SYSFS_MAGIC 0x62656572
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struct vfsmount *sysfs_mount;
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struct super_block * sysfs_sb = NULL;
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kmem_cache_t *sysfs_dir_cachep;
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static struct super_operations sysfs_ops = {
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.statfs = simple_statfs,
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.drop_inode = generic_delete_inode,
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};
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static struct sysfs_dirent sysfs_root = {
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.s_sibling = LIST_HEAD_INIT(sysfs_root.s_sibling),
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.s_children = LIST_HEAD_INIT(sysfs_root.s_children),
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.s_element = NULL,
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.s_type = SYSFS_ROOT,
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.s_iattr = NULL,
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};
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static int sysfs_fill_super(struct super_block *sb, void *data, int silent)
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{
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struct inode *inode;
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struct dentry *root;
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sb->s_blocksize = PAGE_CACHE_SIZE;
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sb->s_blocksize_bits = PAGE_CACHE_SHIFT;
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sb->s_magic = SYSFS_MAGIC;
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sb->s_op = &sysfs_ops;
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sb->s_time_gran = 1;
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sysfs_sb = sb;
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inode = sysfs_new_inode(S_IFDIR | S_IRWXU | S_IRUGO | S_IXUGO,
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&sysfs_root);
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if (inode) {
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inode->i_op = &sysfs_dir_inode_operations;
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inode->i_fop = &sysfs_dir_operations;
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/* directory inodes start off with i_nlink == 2 (for "." entry) */
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inode->i_nlink++;
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} else {
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pr_debug("sysfs: could not get root inode\n");
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return -ENOMEM;
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}
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root = d_alloc_root(inode);
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if (!root) {
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pr_debug("%s: could not get root dentry!\n",__FUNCTION__);
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iput(inode);
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return -ENOMEM;
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}
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root->d_fsdata = &sysfs_root;
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sb->s_root = root;
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return 0;
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}
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static int sysfs_get_sb(struct file_system_type *fs_type,
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int flags, const char *dev_name, void *data, struct vfsmount *mnt)
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{
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return get_sb_single(fs_type, flags, data, sysfs_fill_super, mnt);
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}
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static struct file_system_type sysfs_fs_type = {
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.name = "sysfs",
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.get_sb = sysfs_get_sb,
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.kill_sb = kill_litter_super,
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};
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int __init sysfs_init(void)
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{
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int err = -ENOMEM;
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sysfs_dir_cachep = kmem_cache_create("sysfs_dir_cache",
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sizeof(struct sysfs_dirent),
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0, 0, NULL, NULL);
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if (!sysfs_dir_cachep)
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goto out;
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err = register_filesystem(&sysfs_fs_type);
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if (!err) {
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sysfs_mount = kern_mount(&sysfs_fs_type);
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if (IS_ERR(sysfs_mount)) {
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printk(KERN_ERR "sysfs: could not mount!\n");
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err = PTR_ERR(sysfs_mount);
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sysfs_mount = NULL;
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unregister_filesystem(&sysfs_fs_type);
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goto out_err;
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}
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} else
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goto out_err;
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out:
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return err;
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out_err:
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kmem_cache_destroy(sysfs_dir_cachep);
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sysfs_dir_cachep = NULL;
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goto out;
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}
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