Re: [PATCH 4/4] erofs: add on-disk compression configurations
From: Gao Xiang
Date: Sat Mar 27 2021 - 06:20:52 EST
Hi Chao,
On Sat, Mar 27, 2021 at 05:46:44PM +0800, Chao Yu wrote:
> On 2021/3/27 11:49, Gao Xiang wrote:
> > From: Gao Xiang <hsiangkao@xxxxxxxxxx>
> >
> > Add a bitmap for available compression algorithms and a variable-sized
> > on-disk table for compression options in preparation for upcoming big
> > pcluster and LZMA algorithm, which follows the end of super block.
> >
> > To parse the compression options, the bitmap is scanned one by one.
> > For each available algorithm, there is data followed by 2-byte `length'
> > correspondingly (it's enough for most cases, or entire fs blocks should
> > be used.)
> >
> > With such available algorithm bitmap, kernel itself can also refuse to
> > mount such filesystem if any unsupported compression algorithm exists.
> >
> > Signed-off-by: Gao Xiang <hsiangkao@xxxxxxxxxx>
> > ---
> > fs/erofs/decompressor.c | 2 +-
> > fs/erofs/erofs_fs.h | 16 +++--
> > fs/erofs/internal.h | 5 +-
> > fs/erofs/super.c | 145 +++++++++++++++++++++++++++++++++++++++-
> > 4 files changed, 161 insertions(+), 7 deletions(-)
> >
> > diff --git a/fs/erofs/decompressor.c b/fs/erofs/decompressor.c
> > index 97538ff24a19..27aa6a99b371 100644
> > --- a/fs/erofs/decompressor.c
> > +++ b/fs/erofs/decompressor.c
> > @@ -41,7 +41,7 @@ int z_erofs_load_lz4_config(struct super_block *sb,
> > }
> > distance = le16_to_cpu(lz4->max_distance);
> > } else {
> > - distance = le16_to_cpu(dsb->lz4_max_distance);
> > + distance = le16_to_cpu(dsb->u1.lz4_max_distance);
> > }
> > EROFS_SB(sb)->lz4.max_distance_pages = distance ?
> > diff --git a/fs/erofs/erofs_fs.h b/fs/erofs/erofs_fs.h
> > index 1322ae63944b..ef3f8a99aa5f 100644
> > --- a/fs/erofs/erofs_fs.h
> > +++ b/fs/erofs/erofs_fs.h
> > @@ -18,15 +18,18 @@
> > * be incompatible with this kernel version.
> > */
> > #define EROFS_FEATURE_INCOMPAT_LZ4_0PADDING 0x00000001
> > -#define EROFS_ALL_FEATURE_INCOMPAT EROFS_FEATURE_INCOMPAT_LZ4_0PADDING
> > +#define EROFS_FEATURE_INCOMPAT_COMPR_CFGS 0x00000002
> > +#define EROFS_ALL_FEATURE_INCOMPAT \
> > + (EROFS_FEATURE_INCOMPAT_LZ4_0PADDING | \
> > + EROFS_FEATURE_INCOMPAT_COMPR_CFGS)
> > -/* 128-byte erofs on-disk super block */
> > +/* erofs on-disk super block (currently 128 bytes) */
> > struct erofs_super_block {
> > __le32 magic; /* file system magic number */
> > __le32 checksum; /* crc32c(super_block) */
> > __le32 feature_compat;
> > __u8 blkszbits; /* support block_size == PAGE_SIZE only */
> > - __u8 reserved;
> > + __u8 sb_extslots; /* superblock size = 128 + sb_extslots * 16 */
> > __le16 root_nid; /* nid of root directory */
> > __le64 inos; /* total valid ino # (== f_files - f_favail) */
> > @@ -39,7 +42,11 @@ struct erofs_super_block {
> > __u8 uuid[16]; /* 128-bit uuid for volume */
> > __u8 volume_name[16]; /* volume name */
> > __le32 feature_incompat;
> > - __le16 lz4_max_distance;
> > + union {
> > + /* bitmap for available compression algorithms */
> > + __le16 available_compr_algs;
> > + __le16 lz4_max_distance;
> > + } __packed u1;
> > __u8 reserved2[42];
> > };
> > @@ -195,6 +202,7 @@ enum {
> > Z_EROFS_COMPRESSION_LZ4 = 0,
> > Z_EROFS_COMPRESSION_MAX
> > };
> > +#define Z_EROFS_ALL_COMPR_ALGS (1 << (Z_EROFS_COMPRESSION_MAX - 1))
> > /* 14 bytes (+ length field = 16 bytes) */
> > struct z_erofs_lz4_cfgs {
> > diff --git a/fs/erofs/internal.h b/fs/erofs/internal.h
> > index 46b977f348eb..f3fa895d809f 100644
> > --- a/fs/erofs/internal.h
> > +++ b/fs/erofs/internal.h
> > @@ -75,6 +75,7 @@ struct erofs_sb_info {
> > struct xarray managed_pslots;
> > unsigned int shrinker_run_no;
> > + u16 available_compr_algs;
> > /* pseudo inode to manage cached pages */
> > struct inode *managed_cache;
> > @@ -90,6 +91,7 @@ struct erofs_sb_info {
> > /* inode slot unit size in bit shift */
> > unsigned char islotbits;
> > + u32 sb_size; /* total superblock size */
> > u32 build_time_nsec;
> > u64 build_time;
> > @@ -233,6 +235,7 @@ static inline bool erofs_sb_has_##name(struct erofs_sb_info *sbi) \
> > }
> > EROFS_FEATURE_FUNCS(lz4_0padding, incompat, INCOMPAT_LZ4_0PADDING)
> > +EROFS_FEATURE_FUNCS(compr_cfgs, incompat, INCOMPAT_COMPR_CFGS)
> > EROFS_FEATURE_FUNCS(sb_chksum, compat, COMPAT_SB_CHKSUM)
> > /* atomic flag definitions */
> > @@ -454,7 +457,7 @@ static inline int z_erofs_load_lz4_config(struct super_block *sb,
> > struct erofs_super_block *dsb,
> > struct z_erofs_lz4_cfgs *lz4, int len)
> > {
> > - if (lz4 || dsb->lz4_max_distance) {
> > + if (lz4 || dsb->u1.lz4_max_distance) {
> > erofs_err(sb, "lz4 algorithm isn't enabled");
> > return -EINVAL;
> > }
> > diff --git a/fs/erofs/super.c b/fs/erofs/super.c
> > index 1ca8da3f2125..c5e3039f51bf 100644
> > --- a/fs/erofs/super.c
> > +++ b/fs/erofs/super.c
> > @@ -122,6 +122,138 @@ static bool check_layout_compatibility(struct super_block *sb,
> > return true;
> > }
> > +#ifdef CONFIG_EROFS_FS_ZIP
> > +/* read variable-sized metadata, offset will be aligned by 4-byte */
> > +static void *erofs_read_metadata(struct super_block *sb, struct page **pagep,
> > + erofs_off_t *offset, int *lengthp)
> > +{
> > + struct page *page = *pagep;
> > + u8 *buffer, *ptr;
> > + int len, i, cnt;
> > + erofs_blk_t blk;
> > +
> > + *offset = round_up(*offset, 4);
> > + blk = erofs_blknr(*offset);
> > +
> > + if (!page || page->index != blk) {
> > + if (page) {
> > + unlock_page(page);
> > + put_page(page);
> > + }
> > + page = erofs_get_meta_page(sb, blk);
> > + if (IS_ERR(page))
> > + goto err_nullpage;
> > + }
> > +
> > + ptr = kmap(page);
> > + len = le16_to_cpu(*(__le16 *)&ptr[erofs_blkoff(*offset)]);
> > + if (!len)
> > + len = U16_MAX + 1;
> > + buffer = kmalloc(len, GFP_KERNEL);
> > + if (!buffer) {
> > + buffer = ERR_PTR(-ENOMEM);
>
> Caller expects valid page w/o kmapped or a NULL page, right? it needs
> to call kunmap() here? or out label can be relocated above kunmap()?
Yeah, I misplaced it by mistake, thanks for pointing out!
Thanks,
Gao Xiang
>
> Thanks,
>