Setting ->s_dev to a char device (Was: Re: [PATCH v2] ubifs: allow userspace to map mounts to volumes)
Richard Weinberger
richard at nod.at
Mon May 29 04:50:30 PDT 2017
CC'ing VFS folks
Am 29.05.2017 um 09:22 schrieb Rabin Vincent:
> From: Rabin Vincent <rabinv at axis.com>
>
> There currently appears to be no way for userspace to find out the
> underlying volume number for a mounted ubifs file system, since ubifs
> uses anonymous block devices. The volume name is present in
> /proc/mounts but UBI volumes can be renamed after the volume has been
> mounted.
>
> To remedy this, provide a directory in /sys/fs/ubifs named after the
> underlying anonymous block device's number (obtainable by userspace via
> stat(2)) and provide a link named "ubi" to the underlying UBI volume.
I wonder whether it would make more sense to just assign the character device
number of the UBI volume to ->s_dev.
Then userspace can query the underlying device without additional sysfs
magic.
Sure if userspace expects a block number from UBIFS it will get confused.
Comments?
> # mount | head -1
> ubi0:rootfs on / type ubifs (rw,relatime)
> # ubirename /dev/ubi0 rootfs foo
> # mount | head -1
> ubi0:rootfs on / type ubifs (rw,relatime)
> # stat /
> File: /
> Size: 1520 Blocks: 0 IO Block: 4096 directory
> Device: dh/13d Inode: 1 Links: 18
> ...
> # ls -l /sys/fs/ubifs/
> drwxr-xr-x 2 root root 0 May 23 09:57 0:13
> drwxr-xr-x 2 root root 0 May 23 09:57 0:17
> # ls -l /sys/fs/ubifs/0\:13/
> lrwxrwxrwx 1 root root 0 May 23 11:45 ubi
> -> ../../../devices/virtual/ubi/ubi0/ubi0_10
>
> Signed-off-by: Rabin Vincent <rabinv at axis.com>
> ---
> v2: export symbol to fix module build
>
> Documentation/ABI/testing/sysfs-fs-ubifs | 6 +++
> drivers/mtd/ubi/kapi.c | 13 +++++++
> fs/ubifs/Makefile | 2 +-
> fs/ubifs/super.c | 16 +++++++-
> fs/ubifs/sysfs.c | 66 ++++++++++++++++++++++++++++++++
> fs/ubifs/sysfs.h | 11 ++++++
> fs/ubifs/ubifs.h | 7 ++++
> include/linux/mtd/ubi.h | 3 ++
> 8 files changed, 122 insertions(+), 2 deletions(-)
> create mode 100644 Documentation/ABI/testing/sysfs-fs-ubifs
> create mode 100644 fs/ubifs/sysfs.c
> create mode 100644 fs/ubifs/sysfs.h
>
> diff --git a/Documentation/ABI/testing/sysfs-fs-ubifs b/Documentation/ABI/testing/sysfs-fs-ubifs
> new file mode 100644
> index 0000000..1735859
> --- /dev/null
> +++ b/Documentation/ABI/testing/sysfs-fs-ubifs
> @@ -0,0 +1,6 @@
> +What: /sys/fs/ubifs/<disk>/ubi
> +Date: May 2017
> +Description:
> + This symbolic link points to the file system's underlying UBI
> + volume. The <disk> is the major:minor numbers of the anonymous
> + block device backing the file system.
> diff --git a/drivers/mtd/ubi/kapi.c b/drivers/mtd/ubi/kapi.c
> index d4b2e87..395dae6 100644
> --- a/drivers/mtd/ubi/kapi.c
> +++ b/drivers/mtd/ubi/kapi.c
> @@ -107,6 +107,19 @@ void ubi_get_volume_info(struct ubi_volume_desc *desc,
> EXPORT_SYMBOL_GPL(ubi_get_volume_info);
>
> /**
> + * ubi_volume_kobject - get kobject for a UBI volume.
> + * @desc: volume descriptor
> + *
> + * Retrieves a pointer to the struct kobject underlying the UBI volume.
> + * The caller must hold a reference to the UBI volume.
> + */
> +struct kobject *ubi_volume_kobj(struct ubi_volume_desc *desc)
> +{
> + return &desc->vol->dev.kobj;
> +}
> +EXPORT_SYMBOL_GPL(ubi_volume_kobj);
> +
> +/**
> * ubi_open_volume - open UBI volume.
> * @ubi_num: UBI device number
> * @vol_id: volume ID
> diff --git a/fs/ubifs/Makefile b/fs/ubifs/Makefile
> index 6f3251c..7bf4689 100644
> --- a/fs/ubifs/Makefile
> +++ b/fs/ubifs/Makefile
> @@ -4,5 +4,5 @@ ubifs-y += shrinker.o journal.o file.o dir.o super.o sb.o io.o
> ubifs-y += tnc.o master.o scan.o replay.o log.o commit.o gc.o orphan.o
> ubifs-y += budget.o find.o tnc_commit.o compress.o lpt.o lprops.o
> ubifs-y += recovery.o ioctl.o lpt_commit.o tnc_misc.o xattr.o debug.o
> -ubifs-y += misc.o
> +ubifs-y += sysfs.o misc.o
> ubifs-$(CONFIG_UBIFS_FS_ENCRYPTION) += crypto.o
> diff --git a/fs/ubifs/super.c b/fs/ubifs/super.c
> index cf4cc99..fdcfefe 100644
> --- a/fs/ubifs/super.c
> +++ b/fs/ubifs/super.c
> @@ -1164,6 +1164,10 @@ static int mount_ubifs(struct ubifs_info *c)
> if (err)
> return err;
>
> + err = ubifs_sysfs_register(c);
> + if (err)
> + goto out_debugging;
> +
> err = check_volume_empty(c);
> if (err)
> goto out_free;
> @@ -1496,6 +1500,8 @@ static int mount_ubifs(struct ubifs_info *c)
> vfree(c->ileb_buf);
> vfree(c->sbuf);
> kfree(c->bottom_up_buf);
> + ubifs_sysfs_unregister(c);
> +out_debugging:
> ubifs_debugging_exit(c);
> return err;
> }
> @@ -1536,6 +1542,7 @@ static void ubifs_umount(struct ubifs_info *c)
> vfree(c->sbuf);
> kfree(c->bottom_up_buf);
> ubifs_debugging_exit(c);
> + ubifs_sysfs_unregister(c);
> }
>
> /**
> @@ -2271,14 +2278,20 @@ static int __init ubifs_init(void)
> if (err)
> goto out_compr;
>
> + err = ubifs_sysfs_init();
> + if (err)
> + goto out_dbg;
> +
> err = register_filesystem(&ubifs_fs_type);
> if (err) {
> pr_err("UBIFS error (pid %d): cannot register file system, error %d",
> current->pid, err);
> - goto out_dbg;
> + goto out_sysfs;
> }
> return 0;
>
> +out_sysfs:
> + ubifs_sysfs_exit();
> out_dbg:
> dbg_debugfs_exit();
> out_compr:
> @@ -2308,6 +2321,7 @@ static void __exit ubifs_exit(void)
> rcu_barrier();
> kmem_cache_destroy(ubifs_inode_slab);
> unregister_filesystem(&ubifs_fs_type);
> + ubifs_sysfs_exit();
> }
> module_exit(ubifs_exit);
>
> diff --git a/fs/ubifs/sysfs.c b/fs/ubifs/sysfs.c
> new file mode 100644
> index 0000000..8f2cba1
> --- /dev/null
> +++ b/fs/ubifs/sysfs.c
> @@ -0,0 +1,66 @@
> +#include <linux/fs.h>
> +
> +#include "ubifs.h"
> +
> +static struct kset *ubifs_kset;
> +
> +static void ubifs_sb_release(struct kobject *kobj)
> +{
> + struct ubifs_info *c = container_of(kobj, struct ubifs_info, kobj);
> +
> + complete(&c->kobj_unregister);
> +}
> +
> +static struct kobj_type ubifs_sb_ktype = {
> + .sysfs_ops = &kobj_sysfs_ops,
> + .release = ubifs_sb_release,
> +};
> +
> +int ubifs_sysfs_register(struct ubifs_info *c)
> +{
> + dev_t devt = c->vfs_sb->s_dev;
> + int ret;
> +
> + c->kobj.kset = ubifs_kset;
> + init_completion(&c->kobj_unregister);
> +
> + ret = kobject_init_and_add(&c->kobj, &ubifs_sb_ktype, NULL,
> + "%u:%u", MAJOR(devt), MINOR(devt));
> + if (ret)
> + goto out_put;
> +
> + ret = sysfs_create_link(&c->kobj, ubi_volume_kobj(c->ubi), "ubi");
> + if (ret)
> + goto out_del;
> +
> + return 0;
> +
> +out_del:
> + kobject_del(&c->kobj);
> +out_put:
> + kobject_put(&c->kobj);
> + wait_for_completion(&c->kobj_unregister);
> + return ret;
> +}
> +
> +void ubifs_sysfs_unregister(struct ubifs_info *c)
> +{
> + sysfs_remove_link(&c->kobj, "ubi");
> + kobject_del(&c->kobj);
> + kobject_put(&c->kobj);
> + wait_for_completion(&c->kobj_unregister);
> +}
> +
> +int __init ubifs_sysfs_init(void)
> +{
> + ubifs_kset = kset_create_and_add("ubifs", NULL, fs_kobj);
> + if (!ubifs_kset)
> + return -ENOMEM;
> +
> + return 0;
> +}
> +
> +void ubifs_sysfs_exit(void)
> +{
> + kset_unregister(ubifs_kset);
> +}
> diff --git a/fs/ubifs/sysfs.h b/fs/ubifs/sysfs.h
> new file mode 100644
> index 0000000..4b7e70b
> --- /dev/null
> +++ b/fs/ubifs/sysfs.h
> @@ -0,0 +1,11 @@
> +#ifndef __UBIFS_SYSFS_H__
> +#define __UBIFS_SYSFS_H__
> +
> +struct ubifs_info;
> +
> +int ubifs_sysfs_init(void);
> +void ubifs_sysfs_exit(void);
> +int ubifs_sysfs_register(struct ubifs_info *c);
> +void ubifs_sysfs_unregister(struct ubifs_info *c);
> +
> +#endif
> diff --git a/fs/ubifs/ubifs.h b/fs/ubifs/ubifs.h
> index 298b4d8..3a3154f 100644
> --- a/fs/ubifs/ubifs.h
> +++ b/fs/ubifs/ubifs.h
> @@ -43,7 +43,10 @@
> #else
> #include <linux/fscrypt_notsupp.h>
> #endif
> +#include <linux/sysfs.h>
> +#include <linux/completion.h>
> #include <linux/random.h>
> +#include "sysfs.h"
> #include "ubifs-media.h"
>
> /* Version of this UBIFS implementation */
> @@ -1216,6 +1219,8 @@ struct ubifs_debug_info;
> * @mount_opts: UBIFS-specific mount options
> *
> * @dbg: debugging-related information
> + * @kobj: kobject for /sys/fs/ubifs/
> + * @kobj_unregister: completion to unregister sysfs kobject
> */
> struct ubifs_info {
> struct super_block *vfs_sb;
> @@ -1446,6 +1451,8 @@ struct ubifs_info {
> struct ubifs_mount_opts mount_opts;
>
> struct ubifs_debug_info *dbg;
> + struct kobject kobj;
> + struct completion kobj_unregister;
> };
>
> extern struct list_head ubifs_infos;
> diff --git a/include/linux/mtd/ubi.h b/include/linux/mtd/ubi.h
> index 1e271cb..d35e84f 100644
> --- a/include/linux/mtd/ubi.h
> +++ b/include/linux/mtd/ubi.h
> @@ -26,6 +26,8 @@
> #include <linux/scatterlist.h>
> #include <mtd/ubi-user.h>
>
> +struct kobject;
> +
> /* All voumes/LEBs */
> #define UBI_ALL -1
>
> @@ -241,6 +243,7 @@ struct ubi_volume_desc *ubi_open_volume(int ubi_num, int vol_id, int mode);
> struct ubi_volume_desc *ubi_open_volume_nm(int ubi_num, const char *name,
> int mode);
> struct ubi_volume_desc *ubi_open_volume_path(const char *pathname, int mode);
> +struct kobject *ubi_volume_kobj(struct ubi_volume_desc *desc);
>
> int ubi_register_volume_notifier(struct notifier_block *nb,
> int ignore_existing);
>
Thanks,
//richard
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