fc4f4be9b5
Patch series "mm/nommu: don't use VM_MAYSHARE for MAP_PRIVATE mappings". Trying to reduce the confusion around VM_SHARED and VM_MAYSHARE first requires !CONFIG_MMU to stop using VM_MAYSHARE for MAP_PRIVATE mappings. CONFIG_MMU only sets VM_MAYSHARE for MAP_SHARED mappings. This paves the way for further VM_MAYSHARE and VM_SHARED cleanups: for example, renaming VM_MAYSHARED to VM_MAP_SHARED to make it cleaner what is actually means. Let's first get the weird case out of the way and not use VM_MAYSHARE in MAP_PRIVATE mappings, using a new VM_MAYOVERLAY flag instead. This patch (of 3): We want to stop using VM_MAYSHARE in private mappings to pave the way for clarifying the semantics of VM_MAYSHARE vs. VM_SHARED and reduce the confusion. While CONFIG_MMU uses VM_MAYSHARE to represent MAP_SHARED, !CONFIG_MMU also sets VM_MAYSHARE for selected R/O private file mappings that are an effective overlay of a file mapping. Let's factor out all relevant VM_MAYSHARE checks in !CONFIG_MMU code into is_nommu_shared_mapping() first. Note that whenever VM_SHARED is set, VM_MAYSHARE must be set as well (unless there is a serious BUG). So there is not need to test for VM_SHARED manually. No functional change intended. Link: https://lkml.kernel.org/r/20230102160856.500584-1-david@redhat.com Link: https://lkml.kernel.org/r/20230102160856.500584-2-david@redhat.com Signed-off-by: David Hildenbrand <david@redhat.com> Cc: Arnd Bergmann <arnd@arndb.de> Cc: David Hildenbrand <david@redhat.com> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: Jens Axboe <axboe@kernel.dk> Cc: Nicolas Pitre <nico@fluxnic.net> Cc: Pavel Begunkov <asml.silence@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
86 lines
2.3 KiB
C
86 lines
2.3 KiB
C
// SPDX-License-Identifier: GPL-2.0-or-later
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/* NOMMU mmap support for RomFS on MTD devices
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*
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* Copyright © 2007 Red Hat, Inc. All Rights Reserved.
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* Written by David Howells (dhowells@redhat.com)
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*/
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#include <linux/mm.h>
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#include <linux/mtd/super.h>
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#include "internal.h"
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/*
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* try to determine where a shared mapping can be made
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* - only supported for NOMMU at the moment (MMU can't doesn't copy private
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* mappings)
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* - attempts to map through to the underlying MTD device
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*/
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static unsigned long romfs_get_unmapped_area(struct file *file,
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unsigned long addr,
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unsigned long len,
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unsigned long pgoff,
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unsigned long flags)
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{
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struct inode *inode = file->f_mapping->host;
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struct mtd_info *mtd = inode->i_sb->s_mtd;
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unsigned long isize, offset, maxpages, lpages;
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int ret;
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if (!mtd)
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return (unsigned long) -ENOSYS;
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/* the mapping mustn't extend beyond the EOF */
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lpages = (len + PAGE_SIZE - 1) >> PAGE_SHIFT;
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isize = i_size_read(inode);
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offset = pgoff << PAGE_SHIFT;
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maxpages = (isize + PAGE_SIZE - 1) >> PAGE_SHIFT;
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if ((pgoff >= maxpages) || (maxpages - pgoff < lpages))
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return (unsigned long) -EINVAL;
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if (addr != 0)
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return (unsigned long) -EINVAL;
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if (len > mtd->size || pgoff >= (mtd->size >> PAGE_SHIFT))
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return (unsigned long) -EINVAL;
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offset += ROMFS_I(inode)->i_dataoffset;
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if (offset >= mtd->size)
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return (unsigned long) -EINVAL;
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/* the mapping mustn't extend beyond the EOF */
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if ((offset + len) > mtd->size)
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len = mtd->size - offset;
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ret = mtd_get_unmapped_area(mtd, len, offset, flags);
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if (ret == -EOPNOTSUPP)
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ret = -ENOSYS;
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return (unsigned long) ret;
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}
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/*
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* permit a R/O mapping to be made directly through onto an MTD device if
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* possible
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*/
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static int romfs_mmap(struct file *file, struct vm_area_struct *vma)
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{
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return is_nommu_shared_mapping(vma->vm_flags) ? 0 : -ENOSYS;
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}
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static unsigned romfs_mmap_capabilities(struct file *file)
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{
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struct mtd_info *mtd = file_inode(file)->i_sb->s_mtd;
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if (!mtd)
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return NOMMU_MAP_COPY;
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return mtd_mmap_capabilities(mtd);
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}
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const struct file_operations romfs_ro_fops = {
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.llseek = generic_file_llseek,
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.read_iter = generic_file_read_iter,
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.splice_read = generic_file_splice_read,
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.mmap = romfs_mmap,
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.get_unmapped_area = romfs_get_unmapped_area,
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.mmap_capabilities = romfs_mmap_capabilities,
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};
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