From e8325399d6e18d2acc670999632a461d424611b9 Mon Sep 17 00:00:00 2001 From: Zhan Xusheng Date: Fri, 21 Aug 2026 09:56:41 +0800 Subject: [PATCH] erofs: support splice() in inode_share mode erofs_ishare_fops routes everything that touches the page cache to the backing file in ->private_data: read_iter clones the iocb onto it, mmap does vma_set_file(), fadvise calls vfs_fadvise() on it. splice_read was left as filemap_splice_read(), which works on the user file's own mapping: it does init_sync_kiocb(&iocb, in), and filemap_get_pages() then takes iocb->ki_filp->f_mapping. So splice() and sendfile() fill the per-inode page cache rather than the shared one. The content is the same either way, since erofs_fill_inode() sets a_ops on that mapping too, which is why this went unnoticed. Two identical 8 MiB files under inode_share, reading one of them with splice(2) alone, in pages: before own 2048 shared 0 after own 0 shared 2048 "own" is cachestat(fd), which reports the file's own mapping; "shared" is mmap()+mincore(), which erofs_ishare_mmap() redirects to the backing file. Read through the backing file, as read_iter already does. Link: https://lore.kernel.org/all/b7dc7192-d586-45a2-bc4a-b41dc681c9bb@linux.alibaba.com/ Signed-off-by: Zhan Xusheng Reviewed-by: Jingbo Xu Reviewed-by: Chao Yu Signed-off-by: Gao Xiang --- fs/erofs/ishare.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/fs/erofs/ishare.c b/fs/erofs/ishare.c index 4c7be60565cb..372e9db8fd8c 100644 --- a/fs/erofs/ishare.c +++ b/fs/erofs/ishare.c @@ -148,6 +148,13 @@ static int erofs_ishare_mmap(struct file *file, struct vm_area_struct *vma) return generic_file_readonly_mmap(file, vma); } +static ssize_t erofs_ishare_splice_read(struct file *in, loff_t *ppos, + struct pipe_inode_info *pipe, + size_t len, unsigned int flags) +{ + return filemap_splice_read(in->private_data, ppos, pipe, len, flags); +} + static int erofs_ishare_fadvise(struct file *file, loff_t offset, loff_t len, int advice) { @@ -161,7 +168,7 @@ const struct file_operations erofs_ishare_fops = { .mmap = erofs_ishare_mmap, .release = erofs_ishare_file_release, .get_unmapped_area = thp_get_unmapped_area, - .splice_read = filemap_splice_read, + .splice_read = erofs_ishare_splice_read, .fadvise = erofs_ishare_fadvise, };