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Commit 4fb5ef08 authored by Hugh Dickins's avatar Hugh Dickins Committed by Linus Torvalds
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tmpfs: support SEEK_DATA and SEEK_HOLE 



It's quite easy for tmpfs to scan the radix_tree to support llseek's new
SEEK_DATA and SEEK_HOLE options: so add them while the minutiae are still
on my mind (in particular, the !PageUptodate-ness of pages fallocated but
still unwritten).

But I don't know who actually uses SEEK_DATA or SEEK_HOLE, and whether it
would be of any use to them on tmpfs.  This code adds 92 lines and 752
bytes on x86_64 - is that bloat or worthwhile?

[akpm@linux-foundation.org: fix warning with CONFIG_TMPFS=n]
Signed-off-by: default avatarHugh Dickins <hughd@google.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Josef Bacik <josef@redhat.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Andreas Dilger <adilger@dilger.ca>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Marco Stornelli <marco.stornelli@gmail.com>
Cc: Jeff liu <jeff.liu@oracle.com>
Cc: Chris Mason <chris.mason@oracle.com>
Cc: Sunil Mushran <sunil.mushran@oracle.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 1aac1400

mm/shmem.c

+93 −1
Original line number Diff line number Diff line
@@ -1674,6 +1674,98 @@ static ssize_t shmem_file_splice_read(struct file *in, loff_t *ppos, 
	return error;

}



/*

 * llseek SEEK_DATA or SEEK_HOLE through the radix_tree.

 */

static pgoff_t shmem_seek_hole_data(struct address_space *mapping,

				    pgoff_t index, pgoff_t end, int origin)

{

	struct page *page;

	struct pagevec pvec;

	pgoff_t indices[PAGEVEC_SIZE];

	bool done = false;

	int i;



	pagevec_init(&pvec, 0);

	pvec.nr = 1;		/* start small: we may be there already */

	while (!done) {

		pvec.nr = shmem_find_get_pages_and_swap(mapping, index,

					pvec.nr, pvec.pages, indices);

		if (!pvec.nr) {

			if (origin == SEEK_DATA)

				index = end;

			break;

		}

		for (i = 0; i < pvec.nr; i++, index++) {

			if (index < indices[i]) {

				if (origin == SEEK_HOLE) {

					done = true;

					break;

				}

				index = indices[i];

			}

			page = pvec.pages[i];

			if (page && !radix_tree_exceptional_entry(page)) {

				if (!PageUptodate(page))

					page = NULL;

			}

			if (index >= end ||

			    (page && origin == SEEK_DATA) ||

			    (!page && origin == SEEK_HOLE)) {

				done = true;

				break;

			}

		}

		shmem_deswap_pagevec(&pvec);

		pagevec_release(&pvec);

		pvec.nr = PAGEVEC_SIZE;

		cond_resched();

	}

	return index;

}



static loff_t shmem_file_llseek(struct file *file, loff_t offset, int origin)

{

	struct address_space *mapping;

	struct inode *inode;

	pgoff_t start, end;

	loff_t new_offset;



	if (origin != SEEK_DATA && origin != SEEK_HOLE)

		return generic_file_llseek_size(file, offset, origin,

							MAX_LFS_FILESIZE);

	mapping = file->f_mapping;

	inode = mapping->host;

	mutex_lock(&inode->i_mutex);

	/* We're holding i_mutex so we can access i_size directly */



	if (offset < 0)

		offset = -EINVAL;

	else if (offset >= inode->i_size)

		offset = -ENXIO;

	else {

		start = offset >> PAGE_CACHE_SHIFT;

		end = (inode->i_size + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;

		new_offset = shmem_seek_hole_data(mapping, start, end, origin);

		new_offset <<= PAGE_CACHE_SHIFT;

		if (new_offset > offset) {

			if (new_offset < inode->i_size)

				offset = new_offset;

			else if (origin == SEEK_DATA)

				offset = -ENXIO;

			else

				offset = inode->i_size;

		}

	}



	if (offset >= 0 && offset != file->f_pos) {

		file->f_pos = offset;

		file->f_version = 0;

	}

	mutex_unlock(&inode->i_mutex);

	return offset;

}



static long shmem_fallocate(struct file *file, int mode, loff_t offset,

							 loff_t len)

{
@@ -2679,7 +2771,7 @@ static const struct address_space_operations shmem_aops = { 
static const struct file_operations shmem_file_operations = {

	.mmap		= shmem_mmap,

#ifdef CONFIG_TMPFS

	.llseek		= generic_file_llseek,

	.llseek		= shmem_file_llseek,

	.read		= do_sync_read,

	.write		= do_sync_write,

	.aio_read	= shmem_file_aio_read,