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Message-ID: <alpine.LNX.2.00.1211281706390.1516@eggly.anvils>
Date: Wed, 28 Nov 2012 17:22:03 -0800 (PST)
From: Hugh Dickins <hughd@...gle.com>
To: Andrew Morton <akpm@...ux-foundation.org>
cc: Theodore Ts'o <tytso@....edu>, Zheng Liu <wenqing.lz@...bao.com>,
Jeff liu <jeff.liu@...cle.com>,
Jim Meyering <jim@...ering.net>,
Paul Eggert <eggert@...ucla.edu>,
Christoph Hellwig <hch@...radead.org>,
Josef Bacik <josef@...hat.com>,
Andi Kleen <andi@...stfloor.org>,
Andreas Dilger <adilger@...ger.ca>,
Dave Chinner <david@...morbit.com>,
Marco Stornelli <marco.stornelli@...il.com>,
Chris Mason <chris.mason@...ionio.com>,
Sunil Mushran <sunil.mushran@...cle.com>,
linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
linux-mm@...ck.org
Subject: [PATCH] tmpfs: support SEEK_DATA and SEEK_HOLE (reprise)
Revert 3.5's f21f8062201f ("tmpfs: revert SEEK_DATA and SEEK_HOLE")
to reinstate 4fb5ef089b28 ("tmpfs: support SEEK_DATA and SEEK_HOLE"),
with the intervening additional arg to generic_file_llseek_size().
In 3.8, ext4 is expected to join btrfs, ocfs2 and xfs with proper
SEEK_DATA and SEEK_HOLE support; and a good case has now been made
for it on tmpfs, so let's join the party.
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).
[akpm@...ux-foundation.org: fix warning with CONFIG_TMPFS=n]
Signed-off-by: Hugh Dickins <hughd@...gle.com>
---
mm/shmem.c | 92 ++++++++++++++++++++++++++++++++++++++++++++++++++-
1 file changed, 91 insertions(+), 1 deletion(-)
--- 3.7-rc7/mm/shmem.c 2012-11-16 19:26:56.388459961 -0800
+++ linux/mm/shmem.c 2012-11-28 15:53:38.788477201 -0800
@@ -1709,6 +1709,96 @@ static ssize_t shmem_file_splice_read(st
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 = file->f_mapping;
+ struct inode *inode = mapping->host;
+ 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, i_size_read(inode));
+ 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)
{
@@ -2580,7 +2670,7 @@ static const struct address_space_operat
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,
--
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