Linux内核，mmap_pgoff在mmap.c的实现

1. mmap_pgoff的系统调用实现如下

SYSCALL_DEFINE6(mmap_pgoff, unsigned long, addr, unsigned long, len,
		unsigned long, prot, unsigned long, flags,
		unsigned long, fd, unsigned long, pgoff)
{
	return ksys_mmap_pgoff(addr, len, prot, flags, fd, pgoff);
}

2. ksys_mmap_pgoff函数

unsigned long ksys_mmap_pgoff(unsigned long addr, unsigned long len,
			      unsigned long prot, unsigned long flags,
			      unsigned long fd, unsigned long pgoff)
{
	struct file *file = NULL;
	unsigned long retval;

	if (!(flags & MAP_ANONYMOUS)) {
		audit_mmap_fd(fd, flags);
		file = fget(fd);
		if (!file)
			return -EBADF;
		if (is_file_hugepages(file)) {
			len = ALIGN(len, huge_page_size(hstate_file(file)));
		} else if (unlikely(flags & MAP_HUGETLB)) {
			retval = -EINVAL;
			goto out_fput;
		}
	} else if (flags & MAP_HUGETLB) {
		struct hstate *hs;

		hs = hstate_sizelog((flags >> MAP_HUGE_SHIFT) & MAP_HUGE_MASK);
		if (!hs)
			return -EINVAL;

		len = ALIGN(len, huge_page_size(hs));
		/*
		 * VM_NORESERVE is used because the reservations will be
		 * taken when vm_ops->mmap() is called
		 */
		file = hugetlb_file_setup(HUGETLB_ANON_FILE, len,
				VM_NORESERVE,
				HUGETLB_ANONHUGE_INODE,
				(flags >> MAP_HUGE_SHIFT) & MAP_HUGE_MASK);
		if (IS_ERR(file))
			return PTR_ERR(file);
	}

	retval = vm_mmap_pgoff(file, addr, len, prot, flags, pgoff);
out_fput:
	if (file)
		fput(file);
	return retval;
}

vm_mmap_pgoff函数

unsigned long vm_mmap_pgoff(struct file *file, unsigned long addr,
	unsigned long len, unsigned long prot,
	unsigned long flag, unsigned long pgoff)
{
	unsigned long ret;
	struct mm_struct *mm = current->mm;
	unsigned long populate;
	LIST_HEAD(uf);

	ret = security_mmap_file(file, prot, flag);
	if (!ret) {
		if (mmap_write_lock_killable(mm))
			return -EINTR;
		ret = do_mmap(file, addr, len, prot, flag, 0, pgoff, &populate,
			      &uf);
		mmap_write_unlock(mm);
		userfaultfd_unmap_complete(mm, &uf);
		if (populate)
			mm_populate(ret, populate);
	}
	return ret;
}

do_mmap函数

/*
 * The caller must write-lock current->mm->mmap_lock.
 */
unsigned long do_mmap(struct file *file, unsigned long addr,
			unsigned long len, unsigned long prot,
			unsigned long flags, vm_flags_t vm_flags,
			unsigned long pgoff, unsigned long *populate,
			struct list_head *uf)
{
	struct mm_struct *mm = current->mm;
	int pkey = 0;

	*populate = 0;

	if (!len)
		return -EINVAL;

	/*
	 * Does the application expect PROT_READ to imply PROT_EXEC?
	 *
	 * (the exception is when the underlying filesystem is noexec
	 *  mounted, in which case we dont add PROT_EXEC.)
	 */
	if ((prot & PROT_READ) && (current->personality & READ_IMPLIES_EXEC))
		if (!(file && path_noexec(&file->f_path)))
			prot |= PROT_EXEC;

	/* force arch specific MAP_FIXED handling in get_unmapped_area */
	if (flags & MAP_FIXED_NOREPLACE)
		flags |= MAP_FIXED;

	if (!(flags & MAP_FIXED))
		addr = round_hint_to_min(addr);

	/* Careful about overflows.. */
	len = PAGE_ALIGN(len);
	if (!len)
		return -ENOMEM;

	/* offset overflow? */
	if ((pgoff + (len >> PAGE_SHIFT)) < pgoff)
		return -EOVERFLOW;

	/* Too many mappings? */
	if (mm->map_count > sysctl_max_map_count)
		return -ENOMEM;

	/* Obtain the address to map to. we verify (or select) it and ensure
	 * that it represents a valid section of the address space.
	 */
	addr = get_unmapped_area(file, addr, len, pgoff, flags);
	if (IS_ERR_VALUE(addr))
		return addr;

	if (flags & MAP_FIXED_NOREPLACE) {
		if (find_vma_intersection(mm, addr, addr + len))
			return -EEXIST;
	}

	if (prot == PROT_EXEC) {
		pkey = execute_only_pkey(mm);
		if (pkey < 0)
			pkey = 0;
	}

	/* Do simple checking here so the lower-level routines won't have
	 * to. we assume access permissions have been handled by the open
	 * of the memory object, so we don't do any here.
	 */
	vm_flags |= calc_vm_prot_bits(prot, pkey) | calc_vm_flag_bits(flags) |
			mm->def_flags | VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC;

	if (flags & MAP_LOCKED)
		if (!can_do_mlock())
			return -EPERM;

	if (!mlock_future_ok(mm, vm_flags, len))
		return -EAGAIN;

	if (file) {
		struct inode *inode = file_inode(file);
		unsigned long flags_mask;

		if (!file_mmap_ok(file, inode, pgoff, len))
			return -EOVERFLOW;

		flags_mask = LEGACY_MAP_MASK | file->f_op->mmap_supported_flags;

		switch (flags & MAP_TYPE) {
		case MAP_SHARED:
			/*
			 * Force use of MAP_SHARED_VALIDATE with non-legacy
			 * flags. E.g. MAP_SYNC is dangerous to use with
			 * MAP_SHARED as you don't know which consistency model
			 * you will get. We silently ignore unsupported flags
			 * with MAP_SHARED to preserve backward compatibility.
			 */
			flags &= LEGACY_MAP_MASK;
			fallthrough;
		case MAP_SHARED_VALIDATE:
			if (flags & ~flags_mask)
				return -EOPNOTSUPP;
			if (prot & PROT_WRITE) {
				if (!(file->f_mode & FMODE_WRITE))
					return -EACCES;
				if (IS_SWAPFILE(file->f_mapping->host))
					return -ETXTBSY;
			}

			/*
			 * Make sure we don't allow writing to an append-only
			 * file..
			 */
			if (IS_APPEND(inode) && (file->f_mode & FMODE_WRITE))
				return -EACCES;

			vm_flags |= VM_SHARED | VM_MAYSHARE;
			if (!(file->f_mode & FMODE_WRITE))
				vm_flags &= ~(VM_MAYWRITE | VM_SHARED);
			fallthrough;
		case MAP_PRIVATE:
			if (!(file->f_mode & FMODE_READ))
				return -EACCES;
			if (path_noexec(&file->f_path)) {
				if (vm_flags & VM_EXEC)
					return -EPERM;
				vm_flags &= ~VM_MAYEXEC;
			}

			if (!file->f_op->mmap)
				return -ENODEV;
			if (vm_flags & (VM_GROWSDOWN|VM_GROWSUP))
				return -EINVAL;
			break;

		default:
			return -EINVAL;
		}
	} else {
		switch (flags & MAP_TYPE) {
		case MAP_SHARED:
			if (vm_flags & (VM_GROWSDOWN|VM_GROWSUP))
				return -EINVAL;
			/*
			 * Ignore pgoff.
			 */
			pgoff = 0;
			vm_flags |= VM_SHARED | VM_MAYSHARE;
			break;
		case MAP_PRIVATE:
			/*
			 * Set pgoff according to addr for anon_vma.
			 */
			pgoff = addr >> PAGE_SHIFT;
			break;
		default:
			return -EINVAL;
		}
	}

	/*
	 * Set 'VM_NORESERVE' if we should not account for the
	 * memory use of this mapping.
	 */
	if (flags & MAP_NORESERVE) {
		/* We honor MAP_NORESERVE if allowed to overcommit */
		if (sysctl_overcommit_memory != OVERCOMMIT_NEVER)
			vm_flags |= VM_NORESERVE;

		/* hugetlb applies strict overcommit unless MAP_NORESERVE */
		if (file && is_file_hugepages(file))
			vm_flags |= VM_NORESERVE;
	}

	addr = mmap_region(file, addr, len, vm_flags, pgoff, uf);
	if (!IS_ERR_VALUE(addr) &&
	    ((vm_flags & VM_LOCKED) ||
	     (flags & (MAP_POPULATE | MAP_NONBLOCK)) == MAP_POPULATE))
		*populate = len;
	return addr;
}

get_unmapped_area函数

do_mmap的函数中的会使用get_unmapped_area获取addr

get_unmapped_area

unsigned long
get_unmapped_area(struct file *file, unsigned long addr, unsigned long len,
		unsigned long pgoff, unsigned long flags)
{
	unsigned long (*get_area)(struct file *, unsigned long,
				  unsigned long, unsigned long, unsigned long);

	unsigned long error = arch_mmap_check(addr, len, flags);
	if (error)
		return error;

	/* Careful about overflows.. */
	if (len > TASK_SIZE)
		return -ENOMEM;

	get_area = current->mm->get_unmapped_area;
	if (file) {
		if (file->f_op->get_unmapped_area)
			get_area = file->f_op->get_unmapped_area;
	} else if (flags & MAP_SHARED) {
		/*
		 * mmap_region() will call shmem_zero_setup() to create a file,
		 * so use shmem's get_unmapped_area in case it can be huge.
		 * do_mmap() will clear pgoff, so match alignment.
		 */
		pgoff = 0;
		get_area = shmem_get_unmapped_area;
	}

	addr = get_area(file, addr, len, pgoff, flags);
	if (IS_ERR_VALUE(addr))
		return addr;

	if (addr > TASK_SIZE - len)
		return -ENOMEM;
	if (offset_in_page(addr))
		return -EINVAL;

	error = security_mmap_addr(addr);
	return error ? error : addr;
}

mmap_region函数

get_unmapped_area获取到addr，之后addr传给mmap_region函数

unsigned long mmap_region(struct file *file, unsigned long addr,
		unsigned long len, vm_flags_t vm_flags, unsigned long pgoff,
		struct list_head *uf)
{
	struct mm_struct *mm = current->mm;
	struct vm_area_struct *vma = NULL;
	struct vm_area_struct *next, *prev, *merge;
	pgoff_t pglen = len >> PAGE_SHIFT;
	unsigned long charged = 0;
	unsigned long end = addr + len;
	unsigned long merge_start = addr, merge_end = end;
	pgoff_t vm_pgoff;
	int error;
	VMA_ITERATOR(vmi, mm, addr);

	/* Check against address space limit. */
	if (!may_expand_vm(mm, vm_flags, len >> PAGE_SHIFT)) {
		unsigned long nr_pages;

		/*
		 * MAP_FIXED may remove pages of mappings that intersects with
		 * requested mapping. Account for the pages it would unmap.
		 */
		nr_pages = count_vma_pages_range(mm, addr, end);

		if (!may_expand_vm(mm, vm_flags,
					(len >> PAGE_SHIFT) - nr_pages))
			return -ENOMEM;
	}

	/* Unmap any existing mapping in the area */
	if (do_vmi_munmap(&vmi, mm, addr, len, uf, false))
		return -ENOMEM;

	/*
	 * Private writable mapping: check memory availability
	 */
	if (accountable_mapping(file, vm_flags)) {
		charged = len >> PAGE_SHIFT;
		if (security_vm_enough_memory_mm(mm, charged))
			return -ENOMEM;
		vm_flags |= VM_ACCOUNT;
	}

	next = vma_next(&vmi);
	prev = vma_prev(&vmi);
	if (vm_flags & VM_SPECIAL) {
		if (prev)
			vma_iter_next_range(&vmi);
		goto cannot_expand;
	}

	/* Attempt to expand an old mapping */
	/* Check next */
	if (next && next->vm_start == end && !vma_policy(next) &&
	    can_vma_merge_before(next, vm_flags, NULL, file, pgoff+pglen,
				 NULL_VM_UFFD_CTX, NULL)) {
		merge_end = next->vm_end;
		vma = next;
		vm_pgoff = next->vm_pgoff - pglen;
	}

	/* Check prev */
	if (prev && prev->vm_end == addr && !vma_policy(prev) &&
	    (vma ? can_vma_merge_after(prev, vm_flags, vma->anon_vma, file,
				       pgoff, vma->vm_userfaultfd_ctx, NULL) :
		   can_vma_merge_after(prev, vm_flags, NULL, file, pgoff,
				       NULL_VM_UFFD_CTX, NULL))) {
		merge_start = prev->vm_start;
		vma = prev;
		vm_pgoff = prev->vm_pgoff;
	} else if (prev) {
		vma_iter_next_range(&vmi);
	}

	/* Actually expand, if possible */
	if (vma &&
	    !vma_expand(&vmi, vma, merge_start, merge_end, vm_pgoff, next)) {
		khugepaged_enter_vma(vma, vm_flags);
		goto expanded;
	}

	if (vma == prev)
		vma_iter_set(&vmi, addr);
cannot_expand:

	/*
	 * Determine the object being mapped and call the appropriate
	 * specific mapper. the address has already been validated, but
	 * not unmapped, but the maps are removed from the list.
	 */
	vma = vm_area_alloc(mm);
	if (!vma) {
		error = -ENOMEM;
		goto unacct_error;
	}

	vma_iter_config(&vmi, addr, end);
	vma->vm_start = addr;
	vma->vm_end = end;
	vm_flags_init(vma, vm_flags);
	vma->vm_page_prot = vm_get_page_prot(vm_flags);
	vma->vm_pgoff = pgoff;

	if (file) {
		if (vm_flags & VM_SHARED) {
			error = mapping_map_writable(file->f_mapping);
			if (error)
				goto free_vma;
		}

		vma->vm_file = get_file(file);
		error = call_mmap(file, vma);
		if (error)
			goto unmap_and_free_vma;

		/*
		 * Expansion is handled above, merging is handled below.
		 * Drivers should not alter the address of the VMA.
		 */
		error = -EINVAL;
		if (WARN_ON((addr != vma->vm_start)))
			goto close_and_free_vma;

		vma_iter_config(&vmi, addr, end);
		/*
		 * If vm_flags changed after call_mmap(), we should try merge
		 * vma again as we may succeed this time.
		 */
		if (unlikely(vm_flags != vma->vm_flags && prev)) {
			merge = vma_merge(&vmi, mm, prev, vma->vm_start,
				    vma->vm_end, vma->vm_flags, NULL,
				    vma->vm_file, vma->vm_pgoff, NULL,
				    NULL_VM_UFFD_CTX, NULL);
			if (merge) {
				/*
				 * ->mmap() can change vma->vm_file and fput
				 * the original file. So fput the vma->vm_file
				 * here or we would add an extra fput for file
				 * and cause general protection fault
				 * ultimately.
				 */
				fput(vma->vm_file);
				vm_area_free(vma);
				vma = merge;
				/* Update vm_flags to pick up the change. */
				vm_flags = vma->vm_flags;
				goto unmap_writable;
			}
		}

		vm_flags = vma->vm_flags;
	} else if (vm_flags & VM_SHARED) {
		error = shmem_zero_setup(vma);
		if (error)
			goto free_vma;
	} else {
		vma_set_anonymous(vma);
	}

	if (map_deny_write_exec(vma, vma->vm_flags)) {
		error = -EACCES;
		goto close_and_free_vma;
	}

	/* Allow architectures to sanity-check the vm_flags */
	error = -EINVAL;
	if (!arch_validate_flags(vma->vm_flags))
		goto close_and_free_vma;

	error = -ENOMEM;
	if (vma_iter_prealloc(&vmi, vma))
		goto close_and_free_vma;

	/* Lock the VMA since it is modified after insertion into VMA tree */
	vma_start_write(vma);
	vma_iter_store(&vmi, vma);
	mm->map_count++;
	if (vma->vm_file) {
		i_mmap_lock_write(vma->vm_file->f_mapping);
		if (vma->vm_flags & VM_SHARED)
			mapping_allow_writable(vma->vm_file->f_mapping);

		flush_dcache_mmap_lock(vma->vm_file->f_mapping);
		vma_interval_tree_insert(vma, &vma->vm_file->f_mapping->i_mmap);
		flush_dcache_mmap_unlock(vma->vm_file->f_mapping);
		i_mmap_unlock_write(vma->vm_file->f_mapping);
	}

	/*
	 * vma_merge() calls khugepaged_enter_vma() either, the below
	 * call covers the non-merge case.
	 */
	khugepaged_enter_vma(vma, vma->vm_flags);

	/* Once vma denies write, undo our temporary denial count */
unmap_writable:
	if (file && vm_flags & VM_SHARED)
		mapping_unmap_writable(file->f_mapping);
	file = vma->vm_file;
	ksm_add_vma(vma);
expanded:
	perf_event_mmap(vma);

	vm_stat_account(mm, vm_flags, len >> PAGE_SHIFT);
	if (vm_flags & VM_LOCKED) {
		if ((vm_flags & VM_SPECIAL) || vma_is_dax(vma) ||
					is_vm_hugetlb_page(vma) ||
					vma == get_gate_vma(current->mm))
			vm_flags_clear(vma, VM_LOCKED_MASK);
		else
			mm->locked_vm += (len >> PAGE_SHIFT);
	}

	if (file)
		uprobe_mmap(vma);

	/*
	 * New (or expanded) vma always get soft dirty status.
	 * Otherwise user-space soft-dirty page tracker won't
	 * be able to distinguish situation when vma area unmapped,
	 * then new mapped in-place (which must be aimed as
	 * a completely new data area).
	 */
	vm_flags_set(vma, VM_SOFTDIRTY);

	vma_set_page_prot(vma);

	validate_mm(mm);
	return addr;

close_and_free_vma:
	if (file && vma->vm_ops && vma->vm_ops->close)
		vma->vm_ops->close(vma);

	if (file || vma->vm_file) {
unmap_and_free_vma:
		fput(vma->vm_file);
		vma->vm_file = NULL;

		vma_iter_set(&vmi, vma->vm_end);
		/* Undo any partial mapping done by a device driver. */
		unmap_region(mm, &vmi.mas, vma, prev, next, vma->vm_start,
			     vma->vm_end, vma->vm_end, true);
	}
	if (file && (vm_flags & VM_SHARED))
		mapping_unmap_writable(file->f_mapping);
free_vma:
	vm_area_free(vma);
unacct_error:
	if (charged)
		vm_unacct_memory(charged);
	validate_mm(mm);
	return error;
}