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 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> --- mm/shmem.c | 65 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 files changed, 65 insertions(+), 0 deletions(-) diff --git a/mm/shmem.c b/mm/shmem.c index d672250..65f7a27 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 +1432,69 @@ static ssize_t shmem_file_splice_read(struct file *in, loff_t *ppos, return error; } +static void shmem_truncate_page(struct inode *inode, pgoff_t index) +{ + loff_t start = index << PAGE_CACHE_SHIFT; + loff_t end = ((index + 1) << PAGE_CACHE_SHIFT) - 1; + shmem_truncate_range(inode, start, end); +} + +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; + + 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_truncate_page(inode, index); + 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 +2350,7 @@ 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 }; -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>