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Message-ID: <b91b9f2c-3a07-4726-95d9-75d36bb59871@linux.alibaba.com>
Date: Fri, 16 May 2025 17:15:07 +0800
From: Gao Xiang <hsiangkao@...ux.alibaba.com>
To: Sheng Yong <shengyong2021@...il.com>, xiang@...nel.org, chao@...nel.org,
zbestahu@...il.com, jefflexu@...ux.alibaba.com, dhavale@...gle.com,
lihongbo22@...wei.com
Cc: linux-erofs@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
Sheng Yong <shengyong1@...omi.com>, Wang Shuai <wangshuai12@...omi.com>
Subject: Re: [PATCH v6] erofs: add 'fsoffset' mount option for file-backed &
bdev-based mounts
Hi Yong,
On 2025/5/16 17:00, Sheng Yong wrote:
...
> diff --git a/Documentation/filesystems/erofs.rst b/Documentation/filesystems/erofs.rst
> index c293f8e37468..b24cb0d5d4d6 100644
> --- a/Documentation/filesystems/erofs.rst
> +++ b/Documentation/filesystems/erofs.rst
> @@ -128,6 +128,7 @@ device=%s Specify a path to an extra device to be used together.
> fsid=%s Specify a filesystem image ID for Fscache back-end.
> domain_id=%s Specify a domain ID in fscache mode so that different images
> with the same blobs under a given domain ID can share storage.
> +fsoffset=%lu Specify image offset for file-backed or bdev-based mounts.
Maybe document it as:
fsoffset=%lu Specify filesystem offset for the primary device.
Since I'm not sure if we need later
fsoffset=%lu,[%lu,...] Specify filesystem offset for all devices.
> =================== =========================================================
>
> Sysfs Entries
> diff --git a/fs/erofs/data.c b/fs/erofs/data.c
> index 2409d2ab0c28..599a44d5d782 100644
> --- a/fs/erofs/data.c
> +++ b/fs/erofs/data.c
> @@ -27,9 +27,12 @@ void erofs_put_metabuf(struct erofs_buf *buf)
>
> void *erofs_bread(struct erofs_buf *buf, erofs_off_t offset, bool need_kmap)
> {
> - pgoff_t index = offset >> PAGE_SHIFT;
> + pgoff_t index;
How about just
pgoff_t index = (offset + buf->off) >> PAGE_SHIFT;
since it's not complex to break it into two statements..
> struct folio *folio = NULL;
>
> + offset += buf->off;
> + index = offset >> PAGE_SHIFT;
> +
> if (buf->page) {
> folio = page_folio(buf->page);
> if (folio_file_page(folio, index) != buf->page)
> @@ -54,6 +57,7 @@ void erofs_init_metabuf(struct erofs_buf *buf, struct super_block *sb)
> struct erofs_sb_info *sbi = EROFS_SB(sb);
>
> buf->file = NULL;
> + buf->off = sbi->dif0.off;
> if (erofs_is_fileio_mode(sbi)) {
> buf->file = sbi->dif0.file; /* some fs like FUSE needs it */
> buf->mapping = buf->file->f_mapping;
> @@ -299,7 +303,7 @@ static int erofs_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
> iomap->private = buf.base;
> } else {
> iomap->type = IOMAP_MAPPED;
> - iomap->addr = mdev.m_pa;
> + iomap->addr = mdev.m_dif->off + mdev.m_pa;
I mean, could we update erofs_init_device() and then
`mdev.pa` is already an number added by `mdev.m_dif->off`...
Is it possible? since mdev.pa is already a device-based
offset.
> if (flags & IOMAP_DAX)
> iomap->addr += mdev.m_dif->dax_part_off;
> }
> diff --git a/fs/erofs/fileio.c b/fs/erofs/fileio.c
> index 60c7cc4c105c..a2c7001ff789 100644
> --- a/fs/erofs/fileio.c
> +++ b/fs/erofs/fileio.c
> @@ -147,7 +147,8 @@ static int erofs_fileio_scan_folio(struct erofs_fileio *io, struct folio *folio)
> if (err)
> break;
> io->rq = erofs_fileio_rq_alloc(&io->dev);
> - io->rq->bio.bi_iter.bi_sector = io->dev.m_pa >> 9;
> + io->rq->bio.bi_iter.bi_sector =
> + (io->dev.m_dif->off + io->dev.m_pa) >> 9;
So we don't need here.
> attached = 0;
> }
> if (!bio_add_folio(&io->rq->bio, folio, len, cur))
> diff --git a/fs/erofs/internal.h b/fs/erofs/internal.h
> index 4ac188d5d894..cd8c738f5eb8 100644
> --- a/fs/erofs/internal.h
> +++ b/fs/erofs/internal.h
> @@ -43,6 +43,7 @@ struct erofs_device_info {
> char *path;
> struct erofs_fscache *fscache;
> struct file *file;
> + u64 off;
> struct dax_device *dax_dev;
> u64 dax_part_off;
Maybe `u64 off, dax_part_off;` here?
Also I'm still not quite sure `off` is unambiguous...
Maybe `dataoff`? not quite sure.
>
> @@ -199,6 +200,7 @@ enum {
> struct erofs_buf {
> struct address_space *mapping;
> struct file *file;
> + u64 off;
> struct page *page;
> void *base;
> };
> diff --git a/fs/erofs/super.c b/fs/erofs/super.c
> index da6ee7c39290..512877d7d855 100644
> --- a/fs/erofs/super.c
> +++ b/fs/erofs/super.c
> @@ -356,7 +356,7 @@ static void erofs_default_options(struct erofs_sb_info *sbi)
>
> enum {
> Opt_user_xattr, Opt_acl, Opt_cache_strategy, Opt_dax, Opt_dax_enum,
> - Opt_device, Opt_fsid, Opt_domain_id, Opt_directio,
> + Opt_device, Opt_fsid, Opt_domain_id, Opt_directio, Opt_fsoffset,
> };
>
> static const struct constant_table erofs_param_cache_strategy[] = {
> @@ -383,6 +383,7 @@ static const struct fs_parameter_spec erofs_fs_parameters[] = {
> fsparam_string("fsid", Opt_fsid),
> fsparam_string("domain_id", Opt_domain_id),
> fsparam_flag_no("directio", Opt_directio),
> + fsparam_u64("fsoffset", Opt_fsoffset),
> {}
> };
>
> @@ -506,6 +507,9 @@ static int erofs_fc_parse_param(struct fs_context *fc,
> errorfc(fc, "%s option not supported", erofs_fs_parameters[opt].name);
> #endif
> break;
> + case Opt_fsoffset:
> + sbi->dif0.off = result.uint_64;
> + break;
> }
> return 0;
> }
> @@ -599,6 +603,10 @@ static int erofs_fc_fill_super(struct super_block *sb, struct fs_context *fc)
> &sbi->dif0.dax_part_off, NULL, NULL);
> }
>
> + if (sbi->dif0.off & ((1 << sbi->blkszbits) - 1))
> + return invalfc(fc, "fsoffset %lld not aligned to block size",
is `sbi->blkszbits` valid here? I think it should be moved down
to "erofs_read_superblock(sb)".
"fsoffset %llu is not aligned to block size %u",
sbi->dif0.off, (1 << sbi->blkszbits)
> + sbi->dif0.off);
If fscache doesn't work, we might need to fail out here too.
> +
> err = erofs_read_superblock(sb);
> if (err)
> return err;
> @@ -947,6 +955,8 @@ static int erofs_show_options(struct seq_file *seq, struct dentry *root)
> if (sbi->domain_id)
> seq_printf(seq, ",domain_id=%s", sbi->domain_id);
> #endif
> + if (sbi->dif0.off)
> + seq_printf(seq, ",fsoffset=%lld", sbi->dif0.off);
> return 0;
> }
>
> diff --git a/fs/erofs/zdata.c b/fs/erofs/zdata.c
> index b8e6b76c23d5..4f910d7ffb2f 100644
> --- a/fs/erofs/zdata.c
> +++ b/fs/erofs/zdata.c
> @@ -1707,7 +1707,8 @@ static void z_erofs_submit_queue(struct z_erofs_frontend *f,
> bio = bio_alloc(mdev.m_bdev, BIO_MAX_VECS,
> REQ_OP_READ, GFP_NOIO);
> bio->bi_end_io = z_erofs_endio;
> - bio->bi_iter.bi_sector = cur >> 9;
> + bio->bi_iter.bi_sector =
> + (mdev.m_dif->off + cur) >> 9;
So we don't need here as well.
Thanks,
Gao Xiang
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