From 0fd169576648452725fa2949bf391d10883d3991 Mon Sep 17 00:00:00 2001 From: Hans de Goede Date: Thu, 12 Dec 2019 15:09:14 +0100 Subject: fs: Add VirtualBox guest shared folder (vboxsf) support VirtualBox hosts can share folders with guests, this commit adds a VFS driver implementing the Linux-guest side of this, allowing folders exported by the host to be mounted under Linux. This driver depends on the guest <-> host IPC functions exported by the vboxguest driver. Acked-by: Christoph Hellwig Signed-off-by: Hans de Goede Signed-off-by: Al Viro --- fs/vboxsf/file.c | 379 +++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 379 insertions(+) create mode 100644 fs/vboxsf/file.c (limited to 'fs/vboxsf/file.c') diff --git a/fs/vboxsf/file.c b/fs/vboxsf/file.c new file mode 100644 index 000000000000..c4ab5996d97a --- /dev/null +++ b/fs/vboxsf/file.c @@ -0,0 +1,379 @@ +// SPDX-License-Identifier: MIT +/* + * VirtualBox Guest Shared Folders support: Regular file inode and file ops. + * + * Copyright (C) 2006-2018 Oracle Corporation + */ + +#include +#include +#include +#include +#include +#include "vfsmod.h" + +struct vboxsf_handle { + u64 handle; + u32 root; + u32 access_flags; + struct kref refcount; + struct list_head head; +}; + +static int vboxsf_file_open(struct inode *inode, struct file *file) +{ + struct vboxsf_inode *sf_i = VBOXSF_I(inode); + struct shfl_createparms params = {}; + struct vboxsf_handle *sf_handle; + u32 access_flags = 0; + int err; + + sf_handle = kmalloc(sizeof(*sf_handle), GFP_KERNEL); + if (!sf_handle) + return -ENOMEM; + + /* + * We check the value of params.handle afterwards to find out if + * the call succeeded or failed, as the API does not seem to cleanly + * distinguish error and informational messages. + * + * Furthermore, we must set params.handle to SHFL_HANDLE_NIL to + * make the shared folders host service use our mode parameter. + */ + params.handle = SHFL_HANDLE_NIL; + if (file->f_flags & O_CREAT) { + params.create_flags |= SHFL_CF_ACT_CREATE_IF_NEW; + /* + * We ignore O_EXCL, as the Linux kernel seems to call create + * beforehand itself, so O_EXCL should always fail. + */ + if (file->f_flags & O_TRUNC) + params.create_flags |= SHFL_CF_ACT_OVERWRITE_IF_EXISTS; + else + params.create_flags |= SHFL_CF_ACT_OPEN_IF_EXISTS; + } else { + params.create_flags |= SHFL_CF_ACT_FAIL_IF_NEW; + if (file->f_flags & O_TRUNC) + params.create_flags |= SHFL_CF_ACT_OVERWRITE_IF_EXISTS; + } + + switch (file->f_flags & O_ACCMODE) { + case O_RDONLY: + access_flags |= SHFL_CF_ACCESS_READ; + break; + + case O_WRONLY: + access_flags |= SHFL_CF_ACCESS_WRITE; + break; + + case O_RDWR: + access_flags |= SHFL_CF_ACCESS_READWRITE; + break; + + default: + WARN_ON(1); + } + + if (file->f_flags & O_APPEND) + access_flags |= SHFL_CF_ACCESS_APPEND; + + params.create_flags |= access_flags; + params.info.attr.mode = inode->i_mode; + + err = vboxsf_create_at_dentry(file_dentry(file), ¶ms); + if (err == 0 && params.handle == SHFL_HANDLE_NIL) + err = (params.result == SHFL_FILE_EXISTS) ? -EEXIST : -ENOENT; + if (err) { + kfree(sf_handle); + return err; + } + + /* the host may have given us different attr then requested */ + sf_i->force_restat = 1; + + /* init our handle struct and add it to the inode's handles list */ + sf_handle->handle = params.handle; + sf_handle->root = VBOXSF_SBI(inode->i_sb)->root; + sf_handle->access_flags = access_flags; + kref_init(&sf_handle->refcount); + + mutex_lock(&sf_i->handle_list_mutex); + list_add(&sf_handle->head, &sf_i->handle_list); + mutex_unlock(&sf_i->handle_list_mutex); + + file->private_data = sf_handle; + return 0; +} + +static void vboxsf_handle_release(struct kref *refcount) +{ + struct vboxsf_handle *sf_handle = + container_of(refcount, struct vboxsf_handle, refcount); + + vboxsf_close(sf_handle->root, sf_handle->handle); + kfree(sf_handle); +} + +static int vboxsf_file_release(struct inode *inode, struct file *file) +{ + struct vboxsf_inode *sf_i = VBOXSF_I(inode); + struct vboxsf_handle *sf_handle = file->private_data; + + /* + * When a file is closed on our (the guest) side, we want any subsequent + * accesses done on the host side to see all changes done from our side. + */ + filemap_write_and_wait(inode->i_mapping); + + mutex_lock(&sf_i->handle_list_mutex); + list_del(&sf_handle->head); + mutex_unlock(&sf_i->handle_list_mutex); + + kref_put(&sf_handle->refcount, vboxsf_handle_release); + return 0; +} + +/* + * Write back dirty pages now, because there may not be any suitable + * open files later + */ +static void vboxsf_vma_close(struct vm_area_struct *vma) +{ + filemap_write_and_wait(vma->vm_file->f_mapping); +} + +static const struct vm_operations_struct vboxsf_file_vm_ops = { + .close = vboxsf_vma_close, + .fault = filemap_fault, + .map_pages = filemap_map_pages, +}; + +static int vboxsf_file_mmap(struct file *file, struct vm_area_struct *vma) +{ + int err; + + err = generic_file_mmap(file, vma); + if (!err) + vma->vm_ops = &vboxsf_file_vm_ops; + + return err; +} + +/* + * Note that since we are accessing files on the host's filesystem, files + * may always be changed underneath us by the host! + * + * The vboxsf API between the guest and the host does not offer any functions + * to deal with this. There is no inode-generation to check for changes, no + * events / callback on changes and no way to lock files. + * + * To avoid returning stale data when a file gets *opened* on our (the guest) + * side, we do a "stat" on the host side, then compare the mtime with the + * last known mtime and invalidate the page-cache if they differ. + * This is done from vboxsf_inode_revalidate(). + * + * When reads are done through the read_iter fop, it is possible to do + * further cache revalidation then, there are 3 options to deal with this: + * + * 1) Rely solely on the revalidation done at open time + * 2) Do another "stat" and compare mtime again. Unfortunately the vboxsf + * host API does not allow stat on handles, so we would need to use + * file->f_path.dentry and the stat will then fail if the file was unlinked + * or renamed (and there is no thing like NFS' silly-rename). So we get: + * 2a) "stat" and compare mtime, on stat failure invalidate the cache + * 2b) "stat" and compare mtime, on stat failure do nothing + * 3) Simply always call invalidate_inode_pages2_range on the range of the read + * + * Currently we are keeping things KISS and using option 1. this allows + * directly using generic_file_read_iter without wrapping it. + * + * This means that only data written on the host side before open() on + * the guest side is guaranteed to be seen by the guest. If necessary + * we may provide other read-cache strategies in the future and make this + * configurable through a mount option. + */ +const struct file_operations vboxsf_reg_fops = { + .llseek = generic_file_llseek, + .read_iter = generic_file_read_iter, + .write_iter = generic_file_write_iter, + .mmap = vboxsf_file_mmap, + .open = vboxsf_file_open, + .release = vboxsf_file_release, + .fsync = noop_fsync, + .splice_read = generic_file_splice_read, +}; + +const struct inode_operations vboxsf_reg_iops = { + .getattr = vboxsf_getattr, + .setattr = vboxsf_setattr +}; + +static int vboxsf_readpage(struct file *file, struct page *page) +{ + struct vboxsf_handle *sf_handle = file->private_data; + loff_t off = page_offset(page); + u32 nread = PAGE_SIZE; + u8 *buf; + int err; + + buf = kmap(page); + + err = vboxsf_read(sf_handle->root, sf_handle->handle, off, &nread, buf); + if (err == 0) { + memset(&buf[nread], 0, PAGE_SIZE - nread); + flush_dcache_page(page); + SetPageUptodate(page); + } else { + SetPageError(page); + } + + kunmap(page); + unlock_page(page); + return err; +} + +static struct vboxsf_handle *vboxsf_get_write_handle(struct vboxsf_inode *sf_i) +{ + struct vboxsf_handle *h, *sf_handle = NULL; + + mutex_lock(&sf_i->handle_list_mutex); + list_for_each_entry(h, &sf_i->handle_list, head) { + if (h->access_flags == SHFL_CF_ACCESS_WRITE || + h->access_flags == SHFL_CF_ACCESS_READWRITE) { + kref_get(&h->refcount); + sf_handle = h; + break; + } + } + mutex_unlock(&sf_i->handle_list_mutex); + + return sf_handle; +} + +static int vboxsf_writepage(struct page *page, struct writeback_control *wbc) +{ + struct inode *inode = page->mapping->host; + struct vboxsf_inode *sf_i = VBOXSF_I(inode); + struct vboxsf_handle *sf_handle; + loff_t off = page_offset(page); + loff_t size = i_size_read(inode); + u32 nwrite = PAGE_SIZE; + u8 *buf; + int err; + + if (off + PAGE_SIZE > size) + nwrite = size & ~PAGE_MASK; + + sf_handle = vboxsf_get_write_handle(sf_i); + if (!sf_handle) + return -EBADF; + + buf = kmap(page); + err = vboxsf_write(sf_handle->root, sf_handle->handle, + off, &nwrite, buf); + kunmap(page); + + kref_put(&sf_handle->refcount, vboxsf_handle_release); + + if (err == 0) { + ClearPageError(page); + /* mtime changed */ + sf_i->force_restat = 1; + } else { + ClearPageUptodate(page); + } + + unlock_page(page); + return err; +} + +static int vboxsf_write_end(struct file *file, struct address_space *mapping, + loff_t pos, unsigned int len, unsigned int copied, + struct page *page, void *fsdata) +{ + struct inode *inode = mapping->host; + struct vboxsf_handle *sf_handle = file->private_data; + unsigned int from = pos & ~PAGE_MASK; + u32 nwritten = len; + u8 *buf; + int err; + + /* zero the stale part of the page if we did a short copy */ + if (!PageUptodate(page) && copied < len) + zero_user(page, from + copied, len - copied); + + buf = kmap(page); + err = vboxsf_write(sf_handle->root, sf_handle->handle, + pos, &nwritten, buf + from); + kunmap(page); + + if (err) { + nwritten = 0; + goto out; + } + + /* mtime changed */ + VBOXSF_I(inode)->force_restat = 1; + + if (!PageUptodate(page) && nwritten == PAGE_SIZE) + SetPageUptodate(page); + + pos += nwritten; + if (pos > inode->i_size) + i_size_write(inode, pos); + +out: + unlock_page(page); + put_page(page); + + return nwritten; +} + +/* + * Note simple_write_begin does not read the page from disk on partial writes + * this is ok since vboxsf_write_end only writes the written parts of the + * page and it does not call SetPageUptodate for partial writes. + */ +const struct address_space_operations vboxsf_reg_aops = { + .readpage = vboxsf_readpage, + .writepage = vboxsf_writepage, + .set_page_dirty = __set_page_dirty_nobuffers, + .write_begin = simple_write_begin, + .write_end = vboxsf_write_end, +}; + +static const char *vboxsf_get_link(struct dentry *dentry, struct inode *inode, + struct delayed_call *done) +{ + struct vboxsf_sbi *sbi = VBOXSF_SBI(inode->i_sb); + struct shfl_string *path; + char *link; + int err; + + if (!dentry) + return ERR_PTR(-ECHILD); + + path = vboxsf_path_from_dentry(sbi, dentry); + if (IS_ERR(path)) + return ERR_CAST(path); + + link = kzalloc(PATH_MAX, GFP_KERNEL); + if (!link) { + __putname(path); + return ERR_PTR(-ENOMEM); + } + + err = vboxsf_readlink(sbi->root, path, PATH_MAX, link); + __putname(path); + if (err) { + kfree(link); + return ERR_PTR(err); + } + + set_delayed_call(done, kfree_link, link); + return link; +} + +const struct inode_operations vboxsf_lnk_iops = { + .get_link = vboxsf_get_link +}; -- cgit