by Gao Xiang

[permalink] [raw]

Subject: Re: [PATCH v9 21/21] erofs: add 'fsid' mount option

On Fri, Apr 15, 2022 at 08:36:14PM +0800, Jeffle Xu wrote:
> Introduce 'fsid' mount option to enable on-demand read sementics, in
> which case, erofs will be mounted from data blobs. Users could specify
> the name of primary data blob by this mount option.
>
> Signed-off-by: Jeffle Xu <[email protected]>

Reviewed-by: Gao Xiang <[email protected]>

Thanks,
Gao Xiang

> ---
> fs/erofs/super.c | 31 ++++++++++++++++++++++++++++++-
> fs/erofs/sysfs.c | 4 ++--
> 2 files changed, 32 insertions(+), 3 deletions(-)
>
> diff --git a/fs/erofs/super.c b/fs/erofs/super.c
> index f68ba929100d..4a623630e1c4 100644
> --- a/fs/erofs/super.c
> +++ b/fs/erofs/super.c
> @@ -371,6 +371,8 @@ static int erofs_read_superblock(struct super_block *sb)
>
> if (erofs_sb_has_ztailpacking(sbi))
> erofs_info(sb, "EXPERIMENTAL compressed inline data feature in use. Use at your own risk!");
> + if (erofs_is_fscache_mode(sb))
> + erofs_info(sb, "EXPERIMENTAL fscache-based on-demand read feature in use. Use at your own risk!");
> out:
> erofs_put_metabuf(&buf);
> return ret;
> @@ -399,6 +401,7 @@ enum {
> Opt_dax,
> Opt_dax_enum,
> Opt_device,
> + Opt_fsid,
> Opt_err
> };
>
> @@ -423,6 +426,7 @@ static const struct fs_parameter_spec erofs_fs_parameters[] = {
> fsparam_flag("dax", Opt_dax),
> fsparam_enum("dax", Opt_dax_enum, erofs_dax_param_enums),
> fsparam_string("device", Opt_device),
> + fsparam_string("fsid", Opt_fsid),
> {}
> };
>
> @@ -518,6 +522,16 @@ static int erofs_fc_parse_param(struct fs_context *fc,
> }
> ++ctx->devs->extra_devices;
> break;
> + case Opt_fsid:
> +#ifdef CONFIG_EROFS_FS_ONDEMAND
> + kfree(ctx->opt.fsid);
> + ctx->opt.fsid = kstrdup(param->string, GFP_KERNEL);
> + if (!ctx->opt.fsid)
> + return -ENOMEM;
> +#else
> + errorfc(fc, "fsid option not supported");
> +#endif
> + break;
> default:
> return -ENOPARAM;
> }
> @@ -604,6 +618,7 @@ static int erofs_fc_fill_super(struct super_block *sb, struct fs_context *fc)
>
> sb->s_fs_info = sbi;
> sbi->opt = ctx->opt;
> + ctx->opt.fsid = NULL;
> sbi->devs = ctx->devs;
> ctx->devs = NULL;
>
> @@ -690,6 +705,11 @@ static int erofs_fc_fill_super(struct super_block *sb, struct fs_context *fc)
>
> static int erofs_fc_get_tree(struct fs_context *fc)
> {
> + struct erofs_fs_context *ctx = fc->fs_private;
> +
> + if (IS_ENABLED(CONFIG_EROFS_FS_ONDEMAND) && ctx->opt.fsid)
> + return get_tree_nodev(fc, erofs_fc_fill_super);
> +
> return get_tree_bdev(fc, erofs_fc_fill_super);
> }
>
> @@ -739,6 +759,7 @@ static void erofs_fc_free(struct fs_context *fc)
> struct erofs_fs_context *ctx = fc->fs_private;
>
> erofs_free_dev_context(ctx->devs);
> + kfree(ctx->opt.fsid);
> kfree(ctx);
> }
>
> @@ -779,7 +800,10 @@ static void erofs_kill_sb(struct super_block *sb)
>
> WARN_ON(sb->s_magic != EROFS_SUPER_MAGIC);
>
> - kill_block_super(sb);
> + if (erofs_is_fscache_mode(sb))
> + generic_shutdown_super(sb);
> + else
> + kill_block_super(sb);
>
> sbi = EROFS_SB(sb);
> if (!sbi)
> @@ -789,6 +813,7 @@ static void erofs_kill_sb(struct super_block *sb)
> fs_put_dax(sbi->dax_dev);
> erofs_fscache_unregister_cookie(&sbi->s_fscache);
> erofs_fscache_unregister_fs(sb);
> + kfree(sbi->opt.fsid);
> kfree(sbi);
> sb->s_fs_info = NULL;
> }
> @@ -938,6 +963,10 @@ static int erofs_show_options(struct seq_file *seq, struct dentry *root)
> seq_puts(seq, ",dax=always");
> if (test_opt(opt, DAX_NEVER))
> seq_puts(seq, ",dax=never");
> +#ifdef CONFIG_EROFS_FS_ONDEMAND
> + if (opt->fsid)
> + seq_printf(seq, ",fsid=%s", opt->fsid);
> +#endif
> return 0;
> }
>
> diff --git a/fs/erofs/sysfs.c b/fs/erofs/sysfs.c
> index f3babf1e6608..c1383e508bbe 100644
> --- a/fs/erofs/sysfs.c
> +++ b/fs/erofs/sysfs.c
> @@ -205,8 +205,8 @@ int erofs_register_sysfs(struct super_block *sb)
>
> sbi->s_kobj.kset = &erofs_root;
> init_completion(&sbi->s_kobj_unregister);
> - err = kobject_init_and_add(&sbi->s_kobj, &erofs_sb_ktype, NULL,
> - "%s", sb->s_id);
> + err = kobject_init_and_add(&sbi->s_kobj, &erofs_sb_ktype, NULL, "%s",
> + erofs_is_fscache_mode(sb) ? sbi->opt.fsid : sb->s_id);
> if (err)
> goto put_sb_kobj;
> return 0;
> --
> 2.27.0

2022-04-22 22:42:52

by Jingbo Xu

[permalink] [raw]

Subject: Re: [PATCH v9 06/21] cachefiles: enable on-demand read mode

On 4/21/22 10:17 PM, David Howells wrote:
> Jeffle Xu <[email protected]> wrote:
>
>> + if (IS_ENABLED(CONFIG_CACHEFILES_ONDEMAND) &&
>> + !strcmp(args, "ondemand")) {
>> + set_bit(CACHEFILES_ONDEMAND_MODE, &cache->flags);
>> + } else if (*args) {
>> + pr_err("'bind' command doesn't take an argument\n");
>
> The error message isn't true if CONFIG_CACHEFILES_ONDEMAND=y. It would be
> better to say "Invalid argument to the 'bind' command".

Right. Or users may gets confused then. Will be fixed in the next version.

>
>> -retry:
>> /* If the caller asked us to seek for data before doing the read, then
>> * we should do that now. If we find a gap, we fill it with zeros.
>> */
>> @@ -120,16 +119,6 @@ static int cachefiles_read(struct netfs_cache_resources *cres,
>> if (read_hole == NETFS_READ_HOLE_FAIL)
>> goto presubmission_error;
>>
>> - if (read_hole == NETFS_READ_HOLE_ONDEMAND) {
>> - ret = cachefiles_ondemand_read(object, off, len);
>> - if (ret)
>> - goto presubmission_error;
>> -
>> - /* fail the read if no progress achieved */
>> - read_hole = NETFS_READ_HOLE_FAIL;
>> - goto retry;
>> - }
>> -
>

Sorry, it's my mistake when doing "git rebase". The previous version
(v8) actually calls cachefiles_ondemand_read() in cachefiles_read().
However as explained in the commit message of patch 5 ("cachefiles:
implement on-demand read"), fscache_read() can only detect if the
requested file range is fully cache miss, whilst it can't detect if it
is partial cache miss, i.e. there's a hole inside the requested file range.

Thus in this patchset (v9), we move the entry of calling
cachefiles_ondemand_read() from cachefiles_read() to
cachefiles_prepare_read(). The above "deletion of newly added code" is
actually reverting the previous change to cachefiles_read(). It was
mistakenly merged to this patch when I was doing "git rebase"...
Actually it should be merged to patch 5 ("cachefiles: implement
on-demand read"), which initially introduce the change to cachefiles_read().

Apologize for the careless mistake...

--
Thanks,
Jeffle