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    SubjectRe: [Patch] tmpfs: add fallocate support
    CC: Lennart Poettering <lennart@poettering.net>
    Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>

    On 2011/11/15 16:42, Amerigo Wang wrote:
    > This patch adds fallocate support to tmpfs. I tested this patch
    > with the following test case,
    >
    > % sudo mount -t tmpfs -o size=100 tmpfs /mnt
    > % touch /mnt/foobar
    > % echo hi> /mnt/foobar
    > % fallocate -o 3 -l 5000 /mnt/foobar
    > fallocate: /mnt/foobar: fallocate failed: No space left on device
    > % fallocate -o 3 -l 3000 /mnt/foobar
    > % ls -l /mnt/foobar
    > -rw-rw-r-- 1 wangcong wangcong 3003 Nov 15 16:10 /mnt/foobar
    > % dd if=/dev/zero of=/mnt/foobar seek=3 bs=1 count=3000
    > 3000+0 records in
    > 3000+0 records out
    > 3000 bytes (3.0 kB) copied, 0.0153224 s, 196 kB/s
    > % hexdump -C /mnt/foobar
    > 00000000 68 69 0a 00 00 00 00 00 00 00 00 00 00 00 00 00 |hi..............|
    > 00000010 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
    > *
    > 00000bb0 00 00 00 00 00 00 00 00 00 00 00 |...........|
    > 00000bbb
    > % cat /mnt/foobar
    > hi
    >
    > Signed-off-by: WANG Cong<amwang@redhat.com>
    >
    > ---
    > diff --git a/mm/shmem.c b/mm/shmem.c
    > index d672250..438b7b8 100644
    > --- a/mm/shmem.c
    > +++ b/mm/shmem.c
    > @@ -30,6 +30,7 @@
    > #include<linux/mm.h>
    > #include<linux/export.h>
    > #include<linux/swap.h>
    > +#include<linux/falloc.h>
    >
    > static struct vfsmount *shm_mnt;
    >
    > @@ -1431,6 +1432,102 @@ static ssize_t shmem_file_splice_read(struct file *in, loff_t *ppos,
    > return error;
    > }
    >
    > +static long shmem_fallocate(struct file *file, int mode,
    > + loff_t offset, loff_t len)
    > +{
    > + struct inode *inode = file->f_path.dentry->d_inode;
    > + struct address_space *mapping = inode->i_mapping;
    > + struct shmem_inode_info *info = SHMEM_I(inode);
    > + struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb);
    > + pgoff_t start = DIV_ROUND_UP(offset, PAGE_CACHE_SIZE);
    > + pgoff_t end = DIV_ROUND_UP((offset + len), PAGE_CACHE_SIZE);
    > + pgoff_t index = start;
    > + gfp_t gfp = mapping_gfp_mask(mapping);
    > + loff_t i_size = i_size_read(inode);
    > + struct page *page = NULL;
    > + int ret;
    > +
    > + if ((offset + len)<= i_size)
    > + return 0;
    > +
    > + if (!(mode& FALLOC_FL_KEEP_SIZE)) {
    > + ret = inode_newsize_ok(inode, (offset + len));
    > + if (ret)
    > + return ret;
    > + }
    > +
    > + if (start == end) {
    > + if (!(mode& FALLOC_FL_KEEP_SIZE))
    > + i_size_write(inode, offset + len);
    > + return 0;
    > + }
    > +
    > + if (shmem_acct_block(info->flags))
    > + return -ENOSPC;
    > +
    > + if (sbinfo->max_blocks) {
    > + unsigned long blocks = (end - index) * BLOCKS_PER_PAGE;
    > + if (blocks + percpu_counter_sum(&sbinfo->used_blocks)
    > + >= sbinfo->max_blocks) {
    > + ret = -ENOSPC;
    > + goto unacct;
    > + }
    > + }
    > +
    > + while (index< end) {
    > + if (sbinfo->max_blocks)
    > + percpu_counter_add(&sbinfo->used_blocks, BLOCKS_PER_PAGE);
    > +
    > + page = shmem_alloc_page(gfp, info, index);
    > + if (!page) {
    > + ret = -ENOMEM;
    > + goto decused;
    > + }
    > +
    > + SetPageSwapBacked(page);
    > + __set_page_locked(page);
    > + ret = mem_cgroup_cache_charge(page, current->mm,
    > + gfp& GFP_RECLAIM_MASK);
    > + if (!ret)
    > + ret = shmem_add_to_page_cache(page, mapping, index,
    > + gfp, NULL);
    > + if (ret)
    > + goto unlock;
    > + lru_cache_add_anon(page);
    > +
    > + spin_lock(&info->lock);
    > + info->alloced++;
    > + inode->i_blocks += BLOCKS_PER_PAGE;
    > + inode->i_ctime = inode->i_mtime = CURRENT_TIME;
    > + shmem_recalc_inode(inode);
    > + spin_unlock(&info->lock);
    > +
    > + clear_highpage(page);
    > + flush_dcache_page(page);
    > + SetPageUptodate(page);
    > + unlock_page(page);
    > + page_cache_release(page);
    > + cond_resched();
    > + index++;
    > + if (!(mode& FALLOC_FL_KEEP_SIZE))
    > + i_size_write(inode, index<< PAGE_CACHE_SHIFT);
    > + }
    > +
    > + goto unacct;
    > +
    > +unlock:
    > + if (page) {
    > + unlock_page(page);
    > + page_cache_release(page);
    > + }
    > +decused:
    > + if (sbinfo->max_blocks)
    > + percpu_counter_sub(&sbinfo->used_blocks, BLOCKS_PER_PAGE);
    > +unacct:
    > + shmem_unacct_blocks(info->flags, 1);
    > + return ret;
    > +}
    > +
    > static int shmem_statfs(struct dentry *dentry, struct kstatfs *buf)
    > {
    > struct shmem_sb_info *sbinfo = SHMEM_SB(dentry->d_sb);
    > @@ -2286,6 +2383,7 @@ static const struct file_operations shmem_file_operations = {
    > .fsync = noop_fsync,
    > .splice_read = shmem_file_splice_read,
    > .splice_write = generic_file_splice_write,
    > + .fallocate = shmem_fallocate,
    > #endif
    > };
    >



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