ramfs文件系统源码

/* file-nommu.c: no-MMU version of ramfs * * Copyright (C) 2005 Red Hat, Inc. All Rights Reserved. * Written by David Howells (dhowells@redhat.com) * * This program is free software; you can redistribute it and/or * modify it under the terms of the GNU General Public License * as published by the Free Software Foundation; either version * 2 of the License, or (at your option) any later version. */ #include <linux/module.h> #include <linux/fs.h> #include <linux/mm.h> #include <linux/pagemap.h> #include <linux/highmem.h> #include <linux/init.h> #include <linux/string.h> #include <linux/backing-dev.h> #include <linux/ramfs.h> #include <linux/pagevec.h> #include <linux/mman.h> #include <linux/sched.h> #include <asm/uaccess.h> #include "internal.h" static int ramfs_nommu_setattr(struct dentry *, struct iattr *); const struct address_space_operations ramfs_aops = { .readpage = simple_readpage, .write_begin = simple_write_begin, .write_end = simple_write_end, .set_page_dirty = __set_page_dirty_no_writeback, }; const struct file_operations ramfs_file_operations = { .mmap = ramfs_nommu_mmap, .get_unmapped_area = ramfs_nommu_get_unmapped_area, .read = do_sync_read, .aio_read = generic_file_aio_read, .write = do_sync_write, .aio_write = generic_file_aio_write, .fsync = simple_sync_file, .splice_read = generic_file_splice_read, .splice_write = generic_file_splice_write, .llseek = generic_file_llseek, }; const struct inode_operations ramfs_file_inode_operations = { .setattr = ramfs_nommu_setattr, .getattr = simple_getattr, }; /*****************************************************************************/ /* * add a contiguous set of pages into a ramfs inode when it's truncated from * size 0 on the assumption that it's going to be used for an mmap of shared * memory */ int ramfs_nommu_expand_for_mapping(struct inode *inode, size_t newsize) { unsigned long npages, xpages, loop, limit; struct page *pages; unsigned order; void *data; int ret; /* make various checks */ order = get_order(newsize); if (unlikely(order >= MAX_ORDER)) return -EFBIG; ret = inode_newsize_ok(inode, newsize); if (ret) return ret; i_size_write(inode, newsize); /* allocate enough contiguous pages to be able to satisfy the * request */ pages = alloc_pages(mapping_gfp_mask(inode->i_mapping), order); if (!pages) return -ENOMEM; /* split the high-order page into an array of single pages */ xpages = 1UL << order; npages = (newsize + PAGE_SIZE - 1) >> PAGE_SHIFT; split_page(pages, order); /* trim off any pages we don't actually require */ for (loop = npages; loop < xpages; loop++) __free_page(pages + loop); /* clear the memory we allocated */ newsize = PAGE_SIZE * npages; data = page_address(pages); memset(data, 0, newsize); /* attach all the pages to the inode's address space */ for (loop = 0; loop < npages; loop++) { struct page *page = pages + loop; ret = add_to_page_cache_lru(page, inode->i_mapping, loop, GFP_KERNEL); if (ret < 0) goto add_error; /* prevent the page from being discarded on memory pressure */ SetPageDirty(page); unlock_page(page); put_page(page); } return 0; add_error: while (loop < npages) __free_page(pages + loop++); return ret; } /*****************************************************************************/ /* * check that file shrinkage doesn't leave any VMAs dangling in midair */ static int ramfs_nommu_check_mappings(struct inode *inode, size_t newsize, size_t size) { struct vm_area_struct *vma; struct prio_tree_iter iter; /* search for VMAs that fall within the dead zone */ vma_prio_tree_foreach(vma, &iter, &inode->i_mapping->i_mmap, newsize >> PAGE_SHIFT, (size + PAGE_SIZE - 1) >> PAGE_SHIFT ) { /* found one - only interested if it's shared out of the page * cache */ if (vma->vm_flags & VM_SHARED) return -ETXTBSY; /* not quite true, but near enough */ } return 0; } /*****************************************************************************/ /* * */ static int ramfs_nommu_resize(struct inode *inode, loff_t newsize, loff_t size) { int ret; /* assume a truncate from zero size is going to be for the purposes of * shared mmap */ if (size == 0) { if (unlikely(newsize >> 32)) return -EFBIG; return ramfs_nommu_expand_for_mapping(inode, newsize); } /* check that a decrease in size doesn't cut off any shared mappings */ if (newsize < size) { ret = ramfs_nommu_check_mappings(inode, newsize, size); if (ret < 0) return ret; } ret = vmtruncate(inode, newsize); return ret; } /*****************************************************************************/ /* * handle a change of attributes * - we're specifically interested in a change of size */ static int ramfs_nommu_setattr(struct dentry *dentry, struct iattr *ia) { struct inode *inode = dentry->d_inode; unsigned int old_ia_valid = ia->ia_valid; int ret = 0; /* POSIX UID/GID verification for setting inode attributes */ ret = inode_change_ok(inode, ia); if (ret) return ret; /* pick out size-changing events */ if (ia->ia_valid & ATTR_SIZE) { loff_t size = i_size_read(inode); if (ia->ia_size != size) { ret = ramfs_nommu_resize(inode, ia->ia_size, size); if (ret < 0 || ia->ia_valid == ATTR_SIZE) goto out; } else { /* we skipped the truncate but must still update * timestamps */ ia->ia_valid |= ATTR_MTIME|ATTR_CTIME; } } ret = inode_setattr(inode, ia); out: ia->ia_valid = old_ia_valid; return ret; } /*****************************************************************************/ /* * try to determine where a shared mapping can be made * - we require that: * - the pages to be mapped must exist * - the pages be physically contiguous in sequence */ unsigned long ramfs_nommu_get_unmapped_area(struct file *file, unsigned long addr, unsigned long len, unsigned long pgoff, unsigned long flags) { unsigned long maxpages, lpages, nr, loop, ret; struct inode *inode = file->f_path.dentry->d_inode; struct page **pages = NULL, **ptr, *page; loff_t isize; if (!(flags & MAP_SHARED)) return addr; /* the mapping mustn't extend beyond the EOF */ lpages = (len + PAGE_SIZE - 1) >> PAGE_SHIFT; isize = i_size_read(inode); ret = -EINVAL; maxpages = (isize + PAGE_SIZE - 1) >> PAGE_SHIFT; if (pgoff >= maxpages) goto out; if (maxpages - pgoff < lpages) goto out; /* gang-find the pages */ ret = -ENOMEM; pages = kzalloc(lpages * sizeof(struct page *), GFP_KERNEL); if (!pages) goto out_free; nr = find_get_pages(inode->i_mapping, pgoff, lpages, pages); if (nr != lpages) goto out_free_pages; /* leave if some pages were missing */ /* check the pages for physical adjacency */ ptr = pages; page = *ptr++; page++; for (loop = lpages; loop > 1; loop--) if (*ptr++ != page++) goto out_free_pages; /* okay - all conditions fulfilled */ ret = (unsigned long) page_address(pages[0]); out_free_pages: ptr = pages; for (loop = nr; loop > 0; loop--) put_page(*ptr++); out_free: kfree(pages); out: return ret; } /*****************************************************************************/ /* * set up a mapping for shared memory segments */ int ramfs_nommu_mmap(struct file *file, struct vm_area_struct *vma) { if (!(vma->vm_flags & VM_SHARED)) return -ENOSYS; file_accessed(file); vma->vm_ops = &generic_file_vm_ops; return 0; }