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Message-ID: <YLmvADDywB9toKpW@google.com>
Date: Thu, 3 Jun 2021 21:41:36 -0700
From: Jaegeuk Kim <jaegeuk@...nel.org>
To: Eric Biggers <ebiggers@...nel.org>
Cc: linux-kernel@...r.kernel.org,
linux-f2fs-devel@...ts.sourceforge.net
Subject: Re: [f2fs-dev] [PATCH] f2fs: clean up /sys/fs/f2fs/<disk>/features
On 06/03, Eric Biggers wrote:
> On Thu, Jun 03, 2021 at 03:08:34PM -0700, Jaegeuk Kim wrote:
> > Let's create /sys/fs/f2fs/<disk>/feature_list/ to meet sysfs rule.
> >
> > Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.org>
> > ---
> > Documentation/ABI/testing/sysfs-fs-f2fs | 18 ++-
> > fs/f2fs/f2fs.h | 3 +
> > fs/f2fs/sysfs.c | 152 +++++++++++++++++++++++-
> > 3 files changed, 168 insertions(+), 5 deletions(-)
> >
> > diff --git a/Documentation/ABI/testing/sysfs-fs-f2fs b/Documentation/ABI/testing/sysfs-fs-f2fs
> > index 5088281e312e..43b2cde80b70 100644
> > --- a/Documentation/ABI/testing/sysfs-fs-f2fs
> > +++ b/Documentation/ABI/testing/sysfs-fs-f2fs
> > @@ -203,7 +203,23 @@ Description: Shows total written kbytes issued to disk.
> > What: /sys/fs/f2fs/<disk>/features
> > Date: July 2017
> > Contact: "Jaegeuk Kim" <jaegeuk@...nel.org>
> > -Description: Shows all enabled features in current device.
> > +Description: <deprecated: should use /sys/fs/f2fs/<disk>/feature_list/
> > + Shows all enabled features in current device.
> > + Supported features:
> > + encryption, blkzoned, extra_attr, projquota, inode_checksum,
> > + flexible_inline_xattr, quota_ino, inode_crtime, lost_found,
> > + verity, sb_checksum, casefold, readonly, compression,
> > + encrypted_casefold, pin_file.
>
> Isn't pin_file a feature of the implementation, not of a particular filesystem
> instance? I.e. something that should go in /sys/fs/f2fs/features/, not here.
Done.
>
> Likewise for encrypted_casefold, as it is implied by encryption && casefold.
I think encrypted_casefold needs to be in both places:
1) kernel support by kconfig, 2) on-disk support by feature support.
>
> > +
> > +What: /sys/fs/f2fs/<disk>/feature_list/
> > +Date: June 2021
> > +Contact: "Jaegeuk Kim" <jaegeuk@...nel.org>
> > +Description: Expand /sys/fs/f2fs/<disk>/features to meet sysfs rule.
> > + Supported features:
> > + encryption, block_zoned, extra_attr, projquota, inode_checksum,
> > + flexible_inline_xattr, quota_ino, inode_crtime, lost_found,
> > + verity, sb_checksum, casefold, readonly, compression,
> > + encrypted_casefold, pin_file.
>
> Is it intentional that the file has "blkzoned" but the directory has
> "blk_zoned"?
I tried to sync this with /sys/fs/f2fs/features/block_zoned. Let me add
a comment in the doc.
>
> Also, your code has another difference -- "project_quota" is used instead of
> "projquota". But that's not mentioned above.
Ditto.
>
> And encrypted_casefold and pin_file don't seem appropriate to include here, as
> mentioned above.
Done.
>
> > @@ -1665,6 +1665,9 @@ struct f2fs_sb_info {
> > struct kobject s_stat_kobj; /* /sys/fs/f2fs/<devname>/stat */
> > struct completion s_stat_kobj_unregister;
> >
> > + struct kobject s_disk_feat_kobj; /* /sys/fs/f2fs/<devname>/feature_list */
> > + struct completion s_disk_feat_kobj_unregister;
>
> This is for a particular filesystem instance, not a disk per se. (A f2fs
> filesystem can use multiple disks.) So having "disk" in the name doesn't make
> sense.
>
> Please use more logical names like s_feature_list_kobj,
> f2fs_sb_feature_list_ktype, f2fs_sb_feat_attrs, etc.
Done.
>
> > static ssize_t f2fs_feature_show(struct f2fs_attr *a,
> > struct f2fs_sb_info *sbi, char *buf)
> > {
> > + unsigned long feat_supp = 0;
> > +
> > switch (a->id) {
> > case FEAT_CRYPTO:
> > + feat_supp |= f2fs_sb_has_encrypt(sbi) ?
> > + (1 << FEAT_CRYPTO) : 0;
> > + fallthrough;
> > case FEAT_BLKZONED:
> > - case FEAT_ATOMIC_WRITE:
> > + feat_supp |= f2fs_sb_has_blkzoned(sbi) ?
> > + (1 << FEAT_BLKZONED) : 0;
> > + fallthrough;
> > case FEAT_EXTRA_ATTR:
> > + feat_supp |= f2fs_sb_has_extra_attr(sbi) ?
> > + (1 << FEAT_EXTRA_ATTR) : 0;
> > + fallthrough;
> > case FEAT_PROJECT_QUOTA:
> > + feat_supp |= f2fs_sb_has_project_quota(sbi) ?
> > + (1 << FEAT_PROJECT_QUOTA) : 0;
> > + fallthrough;
> > case FEAT_INODE_CHECKSUM:
> > + feat_supp |= f2fs_sb_has_inode_chksum(sbi) ?
> > + (1 << FEAT_INODE_CHECKSUM) : 0;
> > + fallthrough;
> > case FEAT_FLEXIBLE_INLINE_XATTR:
> > + feat_supp |= f2fs_sb_has_flexible_inline_xattr(sbi) ?
> > + (1 << FEAT_FLEXIBLE_INLINE_XATTR) : 0;
> > + fallthrough;
> > case FEAT_QUOTA_INO:
> > + feat_supp |= f2fs_sb_has_quota_ino(sbi) ?
> > + (1 << FEAT_QUOTA_INO) : 0;
> > + fallthrough;
> > case FEAT_INODE_CRTIME:
> > + feat_supp |= f2fs_sb_has_inode_crtime(sbi) ?
> > + (1 << FEAT_INODE_CRTIME) : 0;
> > + fallthrough;
> > case FEAT_LOST_FOUND:
> > + feat_supp |= f2fs_sb_has_lost_found(sbi) ?
> > + (1 << FEAT_LOST_FOUND) : 0;
> > + fallthrough;
> > case FEAT_VERITY:
> > + feat_supp |= f2fs_sb_has_verity(sbi) ?
> > + (1 << FEAT_VERITY) : 0;
> > + fallthrough;
> > case FEAT_SB_CHECKSUM:
> > + feat_supp |= f2fs_sb_has_sb_chksum(sbi) ?
> > + (1 << FEAT_SB_CHECKSUM) : 0;
> > + fallthrough;
> > case FEAT_CASEFOLD:
> > + feat_supp |= f2fs_sb_has_casefold(sbi) ?
> > + (1 << FEAT_CASEFOLD) : 0;
> > + fallthrough;
> > case FEAT_COMPRESSION:
> > + feat_supp |= f2fs_sb_has_compression(sbi) ?
> > + (1 << FEAT_COMPRESSION) : 0;
> > + fallthrough;
> > case FEAT_RO:
> > - case FEAT_TEST_DUMMY_ENCRYPTION_V2:
> > + feat_supp |= f2fs_sb_has_readonly(sbi) ?
> > + (1 << FEAT_RO) : 0;
> > + fallthrough;
> > case FEAT_ENCRYPTED_CASEFOLD:
> > - return sprintf(buf, "supported\n");
> > + feat_supp |= (f2fs_sb_has_casefold(sbi) &&
> > + f2fs_sb_has_encrypt(sbi)) ?
> > + (1 << FEAT_ENCRYPTED_CASEFOLD) : 0;
> > + fallthrough;
> > + case FEAT_PIN_FILE:
> > + feat_supp |= (1 << FEAT_PIN_FILE);
> > + fallthrough;
> > + case FEAT_TEST_DUMMY_ENCRYPTION_V2:
> > + case FEAT_ATOMIC_WRITE:
> > + if (!a->offset || feat_supp & (1 << a->id))
> > + return sprintf(buf, "supported\n");
> > }
> > - return 0;
> > + return sprintf(buf, "not supported\n");
> > }
>
> This function doesn't make much sense.
>
> Part of the problem is that the same function is handling both
> /sys/fs/f2fs/features/ and /sys/fs/f2fs/$s_id/feature_list/.
>
> All the former needs is to print "supported", since unsupported is indicated by
> the file not being there at all. So it should simply have its own ->show
> function separate from the one for feature_list/.
>
> And the feature_list/ ones could just store the F2FS_FEATURE_* bit in
> f2fs_attr::id and check for it using F2FS_HAS_FEATURE(). That would be much
> simpler -- no need for the feat_id enum or the long switch statement.
>
> Also for feature_list/ it might be better to use "unsupported" than
> "not supported", so that \<supported\> doesn't match...
Done.
>
> > static struct f2fs_attr f2fs_attr_##_name = { \
> > .attr = {.name = __stringify(_name), .mode = 0444 }, \
> > .show = f2fs_feature_show, \
> > + .offset = 0, \
> > .id = _id, \
> > }
>
> There's no need to use the .offset argument if features/ and $s_id/feature_list/
> just used different ->show functions.
>
> > +#define F2FS_DISK_FEATURE_RO_ATTR(_name, _id) \
>
> F2FS_SB_FEATURE_ATTR would be a much better name, since these pertain to a
> filesystem instance (not necessarily a disk), and all the feature attributes are
> read-only.
Used F2FS_SB_FEATURE_RO_ATTR.
>
> > static int __maybe_unused segment_info_seq_show(struct seq_file *seq,
> > void *offset)
> > {
> > @@ -1149,6 +1279,15 @@ int f2fs_register_sysfs(struct f2fs_sb_info *sbi)
> > if (err)
> > goto put_stat_kobj;
> >
> > + sbi->s_disk_feat_kobj.kset = &f2fs_kset;
> > + init_completion(&sbi->s_disk_feat_kobj_unregister);
> > + err = kobject_init_and_add(&sbi->s_disk_feat_kobj,
> > + &f2fs_disk_feat_ktype,
> > + &sbi->s_kobj, "feature_list");
> > + if (err)
> > + goto put_stat_kobj;
> > +
> > +
> > if (f2fs_proc_root)
> > sbi->s_proc = proc_mkdir(sb->s_id, f2fs_proc_root);
> >
> > @@ -1166,6 +1305,8 @@ int f2fs_register_sysfs(struct f2fs_sb_info *sbi)
> > put_stat_kobj:
> > kobject_put(&sbi->s_stat_kobj);
> > wait_for_completion(&sbi->s_stat_kobj_unregister);
> > + kobject_put(&sbi->s_disk_feat_kobj);
> > + wait_for_completion(&sbi->s_disk_feat_kobj_unregister);
>
> It seems this should go to its own label.
>
> Also, please note that it's very easy to get confused between
> /sys/fs/f2fs/features/, /sys/fs/f2fs/$s_id/features, and
> /sys/fs/f2fs/$s_id/feature_list/. Adding some comments could clarify things a
> lot.
Done.
>
> - Eric
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