On 1/4/22 10:40 PM, Gao Xiang wrote:
> On Mon, Dec 27, 2021 at 08:54:34PM +0800, Jeffle Xu wrote:
>> This patch implements the data plane of reading data from bootstrap blob
>> file over fscache.
>>
>> Be noted that currently compressed layout is not supported yet.
>>
>> Signed-off-by: Jeffle Xu <jefflexu@xxxxxxxxxxxxxxxxx>
>> ---
>> fs/erofs/fscache.c | 91 +++++++++++++++++++++++++++++++++++++++++++++
>> fs/erofs/inode.c | 6 ++-
>> fs/erofs/internal.h | 1 +
>> 3 files changed, 97 insertions(+), 1 deletion(-)
>>
>> diff --git a/fs/erofs/fscache.c b/fs/erofs/fscache.c
>> index 325f5663836b..bfcec831d58a 100644
>> --- a/fs/erofs/fscache.c
>> +++ b/fs/erofs/fscache.c
>> @@ -65,6 +65,97 @@ struct page *erofs_readpage_from_fscache(struct erofs_cookie_ctx *ctx,
>> return page;
>> }
>>
>> +static inline void do_copy_page(struct page *from, struct page *to,
>> + size_t offset, size_t len)
>> +{
>> + char *vfrom, *vto;
>> +
>> + vfrom = kmap_atomic(from);
>> + vto = kmap_atomic(to);
>> + memcpy(vto, vfrom + offset, len);
>> + kunmap_atomic(vto);
>> + kunmap_atomic(vfrom);
>> +}
>> +
>> +static int erofs_fscache_do_readpage(struct file *file, struct page *page)
>> +{
>> + struct inode *inode = page->mapping->host;
>> + struct erofs_inode *vi = EROFS_I(inode);
>> + struct super_block *sb = inode->i_sb;
>> + struct erofs_map_blocks map;
>> + erofs_off_t o_la, pa;
>> + size_t offset, len;
>> + struct page *ipage;
>> + int ret;
>> +
>> + if (erofs_inode_is_data_compressed(vi->datalayout)) {
>> + erofs_info(sb, "compressed layout not supported yet");
>> + return -EOPNOTSUPP;
>> + }
>> +
>> + o_la = page_offset(page);
>> + map.m_la = o_la;
>> +
>> + ret = erofs_map_blocks(inode, &map, EROFS_GET_BLOCKS_RAW);
>> + if (ret)
>> + return ret;
>> +
>> + if (!(map.m_flags & EROFS_MAP_MAPPED)) {
>> + zero_user(page, 0, PAGE_SIZE);
>> + return 0;
>> + }
>> +
>> + /*
>> + * 1) For FLAT_PLAIN/FLAT_INLINE layout, the output map.m_la shall be
>> + * equal to o_la, and the output map.m_pa is exactly the physical
>> + * address of o_la.
>> + * 2) For CHUNK_BASED layout, the output map.m_la is rounded down to the
>> + * nearest chunk boundary, and the output map.m_pa is actually the
>> + * physical address of this chunk boundary. So we need to recalculate
>> + * the actual physical address of o_la.
>> + */
>> + pa = map.m_pa + o_la - map.m_la;
>> +
>> + ipage = erofs_get_meta_page(sb, erofs_blknr(pa));
>> + if (IS_ERR(ipage))
>> + return PTR_ERR(ipage);
>> +
>> + /*
>> + * @offset refers to the page offset inside @ipage.
>> + * 1) Except for the inline layout, the offset shall all be 0, and @pa
>> + * shall be aligned with EROFS_BLKSIZ in this case. Thus we can
>> + * conveniently get the offset from @pa.
>> + * 2) While for the inline layout, the offset may be non-zero. Since
>> + * currently only flat layout supports inline, we can calculate the
>> + * offset from the corresponding physical address.
>> + */
>> + offset = erofs_blkoff(pa);
>> + len = min_t(u64, map.m_llen, PAGE_SIZE);
>> +
>> + do_copy_page(ipage, page, offset, len);
>
> If my understanding is correct, I still have no idea why we need to
> copy data here even if fscache can do direct I/O for us without extra
> efforts.
>
> I think the only case would be tail-packing inline (which should go
> through metadata path), otherwise, all data is block-aligned. So
> fscache can handle it directly.
>
Right, only tail packing need special handling here. Would be fixed in
the next version. Thanks.
--
Thanks,
Jeffle
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