于 2011年11月29日 14:02, KAMEZAWA Hiroyuki 写道:
You can't know whether the 'page' is allocated by alloc_page() in fallocate() or just found as exiting one. Then, yourwill corrupt existing pages in error path. Is it allowed ?
According to the comment, /* * shmem_getpage_gfp - find page in cache, or get from swap, or allocate * * If we allocate a new one we do not mark it dirty. That's up to the * vm. If we swap it in we mark it dirty since we also free the swap * entry since a page cannot live in both the swap and page cache */ so we can know if the page is newly allocated by checking page dirty bit. Or am I missing something? But whoops, I sent a wrong version of this patch, the below one is the correct one. Sorry for this.
Subject: [V4 PATCH 1/2] tmpfs: add fallocate support Systemd needs tmpfs to support fallocate [1], to be able to safely use mmap(), regarding SIGBUS, on files on the /dev/shm filesystem. The glibc fallback loop for -ENOSYS on fallocate is just ugly. This patch adds fallocate support to tmpfs, and as we already have shmem_truncate_range(), it is also easy to add FALLOC_FL_PUNCH_HOLE support too. 1. http://lkml.org/lkml/2011/10/20/275 V3->V4: Handle 'undo' ENOSPC more correctly. V2->V3: a) Read i_size directly after holding i_mutex; b) Call page_cache_release() too after shmem_getpage(); c) Undo previous changes when -ENOSPC. Cc: Pekka Enberg <penberg@xxxxxxxxxx> Cc: Christoph Hellwig <hch@xxxxxx> Cc: Hugh Dickins <hughd@xxxxxxxxxx> Cc: Dave Hansen <dave@xxxxxxxxxxxxxxxxxx> Cc: Lennart Poettering <lennart@xxxxxxxxxxxxxx> Cc: Kay Sievers <kay.sievers@xxxxxxxx> Cc: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx> Signed-off-by: WANG Cong <amwang@xxxxxxxxxx> --- commit ca055ad343a0d629f8f1fad1df30796d2292f6a2 Author: Cong Wang <amwang@xxxxxxxxxx> Date: Wed Nov 23 13:16:26 2011 +0800 tmpfs: add fallocate support --- mm/shmem.c | 90 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 files changed, 90 insertions(+), 0 deletions(-) diff --git a/mm/shmem.c b/mm/shmem.c index d672250..6a6fc66 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; @@ -1016,6 +1017,35 @@ failed: return error; } +static void shmem_putpage_noswap(struct inode *inode, pgoff_t index, bool new) +{ + struct address_space *mapping = inode->i_mapping; + struct shmem_inode_info *info; + struct shmem_sb_info *sbinfo; + struct page *page; + + page = find_lock_page(mapping, index); + + if (page) { + info = SHMEM_I(inode); + sbinfo = SHMEM_SB(inode->i_sb); + shmem_acct_block(info->flags); + if (!new && PageDirty(page)) { + ClearPageDirty(page); + delete_from_page_cache(page); + spin_lock(&info->lock); + info->alloced--; + inode->i_blocks -= BLOCKS_PER_PAGE; + spin_unlock(&info->lock); + } + if (sbinfo->max_blocks) + percpu_counter_add(&sbinfo->used_blocks, -1); + shmem_unacct_blocks(info->flags, 1); + unlock_page(page); + page_cache_release(page); + } +} + static int shmem_fault(struct vm_area_struct *vma, struct vm_fault *vmf) { struct inode *inode = vma->vm_file->f_path.dentry->d_inode; @@ -1431,6 +1461,65 @@ 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; + pgoff_t start = offset >> PAGE_CACHE_SHIFT; + pgoff_t end = DIV_ROUND_UP((offset + len), PAGE_CACHE_SIZE); + pgoff_t index = start; + loff_t i_size; + struct page *page = NULL; + int ret = 0; + + if (IS_SWAPFILE(inode)) + return -ETXTBSY; + + mutex_lock(&inode->i_mutex); + i_size = inode->i_size; + if (mode & FALLOC_FL_PUNCH_HOLE) { + if (!(offset > i_size || (end << PAGE_CACHE_SHIFT) > i_size)) + shmem_truncate_range(inode, offset, + (end << PAGE_CACHE_SHIFT) - 1); + goto unlock; + } + + if (!(mode & FALLOC_FL_KEEP_SIZE)) { + ret = inode_newsize_ok(inode, (offset + len)); + if (ret) + goto unlock; + } + + while (index < end) { + ret = shmem_getpage(inode, index, &page, SGP_WRITE, NULL); + if (ret) { + if (ret == -ENOSPC) + goto undo; + else + goto unlock; + } + if (page) { + unlock_page(page); + page_cache_release(page); + } + index++; + } + if (!(mode & FALLOC_FL_KEEP_SIZE) && (index << PAGE_CACHE_SHIFT) > i_size) + i_size_write(inode, index << PAGE_CACHE_SHIFT); + + goto unlock; + +undo: + while (index > start) { + shmem_putpage_noswap(inode, index, true); + index--; + } + +unlock: + mutex_unlock(&inode->i_mutex); + return ret; +} + static int shmem_statfs(struct dentry *dentry, struct kstatfs *buf) { struct shmem_sb_info *sbinfo = SHMEM_SB(dentry->d_sb); @@ -2286,6 +2375,7 @@ 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 };