On Mon, Apr 29, 2024 at 12:04:24PM -0500, John Groves wrote:
> Start building up from the famfs module operations. This commit
> includes the following:
>
> * Register as a file system
> * Parse mount parameters
> * Allocate or find (and initialize) a superblock via famfs_get_tree()
> * Lookup the host dax device, and bail if it's in use (or not dax)
> * Register as the holder of the dax device if it's available
> * Add Kconfig and Makefile misc to build famfs
> * Add FAMFS_SUPER_MAGIC to include/uapi/linux/magic.h
> * Add export of fs/namei.c:may_open_dev(), which famfs needs to call
> * Update MAINTAINERS file for the fs/famfs/ path
>
> The following exports had to happen to enable famfs:
>
> * This uses the new fs/super.c:kill_char_super() - the other kill*super
> helpers were not quite right.
> * This uses the dev_dax_iomap export of dax_dev_get()
>
> This commit builds but is otherwise too incomplete to run
>
> Signed-off-by: John Groves <j...@groves.net>
> ---
> MAINTAINERS | 1 +
> fs/Kconfig | 2 +
> fs/Makefile | 1 +
> fs/famfs/Kconfig | 10 ++
> fs/famfs/Makefile | 5 +
> fs/famfs/famfs_inode.c | 345 +++++++++++++++++++++++++++++++++++++
> fs/famfs/famfs_internal.h | 36 ++++
> fs/namei.c | 1 +
> include/uapi/linux/magic.h | 1 +
> 9 files changed, 402 insertions(+)
> create mode 100644 fs/famfs/Kconfig
> create mode 100644 fs/famfs/Makefile
> create mode 100644 fs/famfs/famfs_inode.c
> create mode 100644 fs/famfs/famfs_internal.h
>
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 3f2d847dcf01..365d678e2f40 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -8188,6 +8188,7 @@ L: linux-...@vger.kernel.org
> L: linux-fsde...@vger.kernel.org
> S: Supported
> F: Documentation/filesystems/famfs.rst
> +F: fs/famfs
>
> FANOTIFY
> M: Jan Kara <j...@suse.cz>
> diff --git a/fs/Kconfig b/fs/Kconfig
> index a46b0cbc4d8f..53b4629e92a0 100644
> --- a/fs/Kconfig
> +++ b/fs/Kconfig
> @@ -140,6 +140,8 @@ source "fs/autofs/Kconfig"
> source "fs/fuse/Kconfig"
> source "fs/overlayfs/Kconfig"
>
> +source "fs/famfs/Kconfig"
> +
> menu "Caches"
>
> source "fs/netfs/Kconfig"
> diff --git a/fs/Makefile b/fs/Makefile
> index 6ecc9b0a53f2..3393f399a9e9 100644
> --- a/fs/Makefile
> +++ b/fs/Makefile
> @@ -129,3 +129,4 @@ obj-$(CONFIG_EFIVAR_FS) += efivarfs/
> obj-$(CONFIG_EROFS_FS) += erofs/
> obj-$(CONFIG_VBOXSF_FS) += vboxsf/
> obj-$(CONFIG_ZONEFS_FS) += zonefs/
> +obj-$(CONFIG_FAMFS) += famfs/
> diff --git a/fs/famfs/Kconfig b/fs/famfs/Kconfig
> new file mode 100644
> index 000000000000..edb8980820f7
> --- /dev/null
> +++ b/fs/famfs/Kconfig
> @@ -0,0 +1,10 @@
> +
> +
> +config FAMFS
> + tristate "famfs: shared memory file system"
> + depends on DEV_DAX && FS_DAX && DEV_DAX_IOMAP
> + help
> + Support for the famfs file system. Famfs is a dax file system that
> + can support scale-out shared access to fabric-attached memory
> + (e.g. CXL shared memory). Famfs is not a general purpose file system;
> + it is an enabler for data sets in shared memory.
> diff --git a/fs/famfs/Makefile b/fs/famfs/Makefile
> new file mode 100644
> index 000000000000..62230bcd6793
> --- /dev/null
> +++ b/fs/famfs/Makefile
> @@ -0,0 +1,5 @@
> +# SPDX-License-Identifier: GPL-2.0
> +
> +obj-$(CONFIG_FAMFS) += famfs.o
> +
> +famfs-y := famfs_inode.o
> diff --git a/fs/famfs/famfs_inode.c b/fs/famfs/famfs_inode.c
> new file mode 100644
> index 000000000000..61306240fc0b
> --- /dev/null
> +++ b/fs/famfs/famfs_inode.c
> @@ -0,0 +1,345 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * famfs - dax file system for shared fabric-attached memory
> + *
> + * Copyright 2023-2024 Micron Technology, inc
> + *
> + * This file system, originally based on ramfs the dax support from xfs,
> + * is intended to allow multiple host systems to mount a common file system
> + * view of dax files that map to shared memory.
> + */
> +
> +#include <linux/fs.h>
> +#include <linux/time.h>
> +#include <linux/init.h>
> +#include <linux/string.h>
> +#include <linux/parser.h>
> +#include <linux/magic.h>
> +#include <linux/slab.h>
> +#include <linux/fs_context.h>
> +#include <linux/fs_parser.h>
> +#include <linux/dax.h>
> +#include <linux/hugetlb.h>
> +#include <linux/iomap.h>
> +#include <linux/path.h>
> +#include <linux/namei.h>
> +
> +#include "famfs_internal.h"
> +
> +#define FAMFS_DEFAULT_MODE 0755
> +
> +static struct inode *famfs_get_inode(struct super_block *sb,
> + const struct inode *dir,
> + umode_t mode, dev_t dev)
> +{
> + struct inode *inode = new_inode(sb);
> + struct timespec64 tv;
> +
> + if (!inode)
> + return NULL;
> +
> + inode->i_ino = get_next_ino();
> + inode_init_owner(&nop_mnt_idmap, inode, dir, mode);
> + inode->i_mapping->a_ops = &ram_aops;
> + mapping_set_gfp_mask(inode->i_mapping, GFP_HIGHUSER);
> + mapping_set_unevictable(inode->i_mapping);
> + tv = inode_set_ctime_current(inode);
> + inode_set_mtime_to_ts(inode, tv);
> + inode_set_atime_to_ts(inode, tv);
> +
> + switch (mode & S_IFMT) {
> + default:
> + init_special_inode(inode, mode, dev);
> + break;
> + case S_IFREG:
> + inode->i_op = NULL /* famfs_file_inode_operations */;
> + inode->i_fop = NULL /* &famfs_file_operations */;
> + break;
> + case S_IFDIR:
> + inode->i_op = NULL /* famfs_dir_inode_operations */;
> + inode->i_fop = &simple_dir_operations;
> +
> + /* Directory inodes start off with i_nlink == 2 (for ".") */
> + inc_nlink(inode);
> + break;
> + case S_IFLNK:
> + inode->i_op = &page_symlink_inode_operations;
> + inode_nohighmem(inode);
> + break;
> + }
> + return inode;
> +}
> +
> +/*
> + * famfs dax_operations (for char dax)
> + */
> +static int
> +famfs_dax_notify_failure(struct dax_device *dax_dev, u64 offset,
> + u64 len, int mf_flags)
> +{
> + struct super_block *sb = dax_holder(dax_dev);
> + struct famfs_fs_info *fsi = sb->s_fs_info;
> +
> + pr_err("%s: rootdev=%s offset=%lld len=%llu flags=%x\n", __func__,
> + fsi->rootdev, offset, len, mf_flags);
> +
> + return 0;
> +}
> +
> +static const struct dax_holder_operations famfs_dax_holder_ops = {
> + .notify_failure = famfs_dax_notify_failure,
> +};
> +
> +/*****************************************************************************
> + * fs_context_operations
> + */
> +
> +static int
> +famfs_fill_super(struct super_block *sb, struct fs_context *fc)
> +{
> + int rc = 0;
> +
> + sb->s_maxbytes = MAX_LFS_FILESIZE;
> + sb->s_blocksize = PAGE_SIZE;
> + sb->s_blocksize_bits = PAGE_SHIFT;
> + sb->s_magic = FAMFS_SUPER_MAGIC;
> + sb->s_op = NULL /* famfs_super_ops */;
> + sb->s_time_gran = 1;
> +
> + return rc;
> +}
> +
> +static int
> +lookup_daxdev(const char *pathname, dev_t *devno)
> +{
> + struct inode *inode;
> + struct path path;
> + int err;
> +
> + if (!pathname || !*pathname)
> + return -EINVAL;
> +
> + err = kern_path(pathname, LOOKUP_FOLLOW, &path);
> + if (err)
> + return err;
> +
> + inode = d_backing_inode(path.dentry);
> + if (!S_ISCHR(inode->i_mode)) {
> + err = -EINVAL;
> + goto out_path_put;
> + }
> +
> + if (!may_open_dev(&path)) { /* had to export this */
> + err = -EACCES;
> + goto out_path_put;
> + }
> +
> + /* if it's dax, i_rdev is struct dax_device */
> + *devno = inode->i_rdev;
> +
> +out_path_put:
> + path_put(&path);
> + return err;
> +}
> +
> +static int
> +famfs_get_tree(struct fs_context *fc)
> +{
> + struct famfs_fs_info *fsi = fc->s_fs_info;
> + struct dax_device *dax_devp;
> + struct super_block *sb;
> + struct inode *inode;
> + dev_t daxdevno;
> + int err;
> +
> + /* TODO: clean up chatty messages */
> +
> + err = lookup_daxdev(fc->source, &daxdevno);
> + if (err)
> + return err;
> +
> + fsi->daxdevno = daxdevno;
> +
> + /* This will set sb->s_dev=daxdevno */
> + sb = sget_dev(fc, daxdevno);
This will open the dax device as a block device. However, nothing in
your ->kill_sb method or kill_char_super() closes it again. So you're
leaking block device references and leaving unitialized memory around as
you've claimed that device but never ended your claim.
> + if (IS_ERR(sb)) {
> + pr_err("%s: sget_dev error\n", __func__);
> + return PTR_ERR(sb);
> + }
> +
> + if (sb->s_root) {
> + pr_info("%s: found a matching suerblock for %s\n",
> + __func__, fc->source);
> +
> + /* We don't expect to find a match by dev_t; if we do, it must
> + * already be mounted, so we bail
> + */
> + err = -EBUSY;
> + goto deactivate_out;
> + } else {
> + pr_info("%s: initializing new superblock for %s\n",
> + __func__, fc->source);
> + err = famfs_fill_super(sb, fc);
> + if (err)
> + goto deactivate_out;
> + }
> +
> + /* This will fail if it's not a dax device */
> + dax_devp = dax_dev_get(daxdevno);
> + if (!dax_devp) {
> + pr_warn("%s: device %s not found or not dax\n",
> + __func__, fc->source);
> + err = -ENODEV;
> + goto deactivate_out;
> + }
> +
> + err = fs_dax_get(dax_devp, sb, &famfs_dax_holder_ops);
> + if (err) {
> + pr_err("%s: fs_dax_get(%lld) failed\n", __func__,
> (u64)daxdevno);
> + err = -EBUSY;
> + goto deactivate_out;
> + }
> + fsi->dax_devp = dax_devp;
> +
> + inode = famfs_get_inode(sb, NULL, S_IFDIR | fsi->mount_opts.mode, 0);
> + sb->s_root = d_make_root(inode);
> + if (!sb->s_root) {
> + pr_err("%s: d_make_root() failed\n", __func__);
> + err = -ENOMEM;
> + fs_put_dax(fsi->dax_devp, sb);
> + goto deactivate_out;
> + }
> +
> + sb->s_flags |= SB_ACTIVE;
> +
> + WARN_ON(fc->root);
> + fc->root = dget(sb->s_root);
> + return err;
> +
> +deactivate_out:
> + pr_debug("%s: deactivating sb=%llx\n", __func__, (u64)sb);
> + deactivate_locked_super(sb);
> + return err;
> +}
> +
> +/*****************************************************************************/
> +
> +enum famfs_param {
> + Opt_mode,
> + Opt_dax,
> +};
> +
> +const struct fs_parameter_spec famfs_fs_parameters[] = {
> + fsparam_u32oct("mode", Opt_mode),
> + fsparam_string("dax", Opt_dax),
> + {}
> +};
> +
> +static int famfs_parse_param(struct fs_context *fc, struct fs_parameter
> *param)
> +{
> + struct famfs_fs_info *fsi = fc->s_fs_info;
> + struct fs_parse_result result;
> + int opt;
> +
> + opt = fs_parse(fc, famfs_fs_parameters, param, &result);
> + if (opt == -ENOPARAM) {
> + opt = vfs_parse_fs_param_source(fc, param);
> + if (opt != -ENOPARAM)
> + return opt;
This shouldn't be needed. The VFS will handle all that for you.
> +
> + return 0;
> + }
> + if (opt < 0)
> + return opt;
> +
> + switch (opt) {
> + case Opt_mode:
> + fsi->mount_opts.mode = result.uint_32 & S_IALLUGO;
> + break;
> + case Opt_dax:
> + if (strcmp(param->string, "always"))
> + pr_notice("%s: invalid dax mode %s\n",
> + __func__, param->string);
> + break;
> + }
> +
> + return 0;
> +}
> +
> +static void famfs_free_fc(struct fs_context *fc)
> +{
> + struct famfs_fs_info *fsi = fc->s_fs_info;
> +
> + if (fsi && fsi->rootdev)
> + kfree(fsi->rootdev);
Dead code since rootdev is unused an unset?
> +
> + kfree(fsi);
> +}
> +
> +static const struct fs_context_operations famfs_context_ops = {
> + .free = famfs_free_fc,
> + .parse_param = famfs_parse_param,
> + .get_tree = famfs_get_tree,
> +};
> +
> +static int famfs_init_fs_context(struct fs_context *fc)
> +{
> + struct famfs_fs_info *fsi;
> +
> + fsi = kzalloc(sizeof(*fsi), GFP_KERNEL);
> + if (!fsi)
> + return -ENOMEM;
> +
> + fsi->mount_opts.mode = FAMFS_DEFAULT_MODE;
> + fc->s_fs_info = fsi;
> + fc->ops = &famfs_context_ops;
> + return 0;
> +}
> +
> +static void famfs_kill_sb(struct super_block *sb)
> +{
> + struct famfs_fs_info *fsi = sb->s_fs_info;
> +
> + if (fsi->dax_devp)
> + fs_put_dax(fsi->dax_devp, sb);
> + if (fsi && fsi->rootdev)
> + kfree(fsi->rootdev);
> + kfree(fsi);
> + sb->s_fs_info = NULL;
> +
> + kill_char_super(sb); /* new */
> +}
Can likely just be
static void famfs_kill_sb(struct super_block *sb)
{
struct famfs_fs_info *fsi = sb->s_fs_info;
generic_shutdown_super(sb);
if (sb->s_bdev_file)
bdev_fput(sb->s_bdev_file);
if (fsi->dax_devp)
fs_put_dax(fsi->dax_devp, sb);
kfree(fsi);
}
and then you don't need any custom helpers at all.
> +
> +#define MODULE_NAME "famfs"
> +static struct file_system_type famfs_fs_type = {
> + .name = MODULE_NAME,
> + .init_fs_context = famfs_init_fs_context,
> + .parameters = famfs_fs_parameters,
> + .kill_sb = famfs_kill_sb,
> + .fs_flags = FS_USERNS_MOUNT,
Sorry, no. This should not be mountable by unprivileged users and
containers if it's using a real device and especially not since it's not
even a mature filesystem.
> +};
> +
> +/******************************************************************************
> + * Module stuff
> + */
> +static int __init init_famfs_fs(void)
> +{
> + int rc;
> +
> + rc = register_filesystem(&famfs_fs_type);
> +
> + return rc;
> +}
> +
> +static void
> +__exit famfs_exit(void)
> +{
> + unregister_filesystem(&famfs_fs_type);
> + pr_info("%s: unregistered\n", __func__);
> +}
> +
> +fs_initcall(init_famfs_fs);
> +module_exit(famfs_exit);
> +
> +MODULE_AUTHOR("John Groves, Micron Technology");
> +MODULE_LICENSE("GPL");
> diff --git a/fs/famfs/famfs_internal.h b/fs/famfs/famfs_internal.h
> new file mode 100644
> index 000000000000..951b32ec4fbd
> --- /dev/null
> +++ b/fs/famfs/famfs_internal.h
> @@ -0,0 +1,36 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * famfs - dax file system for shared fabric-attached memory
> + *
> + * Copyright 2023-2024 Micron Technology, Inc.
> + *
> + * This file system, originally based on ramfs the dax support from xfs,
> + * is intended to allow multiple host systems to mount a common file system
> + * view of dax files that map to shared memory.
> + */
> +#ifndef FAMFS_INTERNAL_H
> +#define FAMFS_INTERNAL_H
> +
> +struct famfs_mount_opts {
> + umode_t mode;
> +};
> +
> +/**
> + * @famfs_fs_info
> + *
> + * @mount_opts: the mount options
> + * @dax_devp: The underlying character devdax device
> + * @rootdev: Dax device path used in mount
> + * @daxdevno: Dax device dev_t
> + * @deverror: True if the dax device has called our notify_failure entry
> + * point, or if other "shutdown" conditions exist
> + */
> +struct famfs_fs_info {
> + struct famfs_mount_opts mount_opts;
> + struct dax_device *dax_devp;
> + char *rootdev;
> + dev_t daxdevno;
> + bool deverror;
> +};
> +
> +#endif /* FAMFS_INTERNAL_H */
> diff --git a/fs/namei.c b/fs/namei.c
> index c5b2a25be7d0..f24b268473cd 100644
> --- a/fs/namei.c
> +++ b/fs/namei.c
> @@ -3229,6 +3229,7 @@ bool may_open_dev(const struct path *path)
> return !(path->mnt->mnt_flags & MNT_NODEV) &&
> !(path->mnt->mnt_sb->s_iflags & SB_I_NODEV);
> }
> +EXPORT_SYMBOL(may_open_dev);
>
> static int may_open(struct mnt_idmap *idmap, const struct path *path,
> int acc_mode, int flag)
> diff --git a/include/uapi/linux/magic.h b/include/uapi/linux/magic.h
> index 1b40a968ba91..e9bdd6a415e2 100644
> --- a/include/uapi/linux/magic.h
> +++ b/include/uapi/linux/magic.h
> @@ -37,6 +37,7 @@
> #define HOSTFS_SUPER_MAGIC 0x00c0ffee
> #define OVERLAYFS_SUPER_MAGIC 0x794c7630
> #define FUSE_SUPER_MAGIC 0x65735546
> +#define FAMFS_SUPER_MAGIC 0x87b282ff
>
> #define MINIX_SUPER_MAGIC 0x137F /* minix v1 fs, 14 char names */
> #define MINIX_SUPER_MAGIC2 0x138F /* minix v1 fs, 30 char names */
> --
> 2.43.0
>
