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    Subject[PATCH 10/13] overlayfs: implement show_options
    Date
    From: Erez Zadok <ezk@fsl.cs.sunysb.edu>

    This is useful because of the stacking nature of overlayfs. Users like to
    find out (via /proc/mounts) which lower/upper directory were used at mount
    time.

    Signed-off-by: Erez Zadok <ezk@cs.sunysb.edu>
    Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
    ---
    fs/overlayfs/super.c | 76 +++++++++++++++++++++++++++++++++++-----------------
    1 file changed, 51 insertions(+), 25 deletions(-)

    diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
    index 8b77f3f45579..fcbd92a14e69 100644
    --- a/fs/overlayfs/super.c
    +++ b/fs/overlayfs/super.c
    @@ -17,6 +17,7 @@
    #include <linux/module.h>
    #include <linux/sched.h>
    #include <linux/statfs.h>
    +#include <linux/seq_file.h>
    #include "overlayfs.h"

    MODULE_AUTHOR("Miklos Szeredi <miklos@szeredi.hu>");
    @@ -25,13 +26,23 @@ MODULE_LICENSE("GPL");

    #define OVERLAYFS_SUPER_MAGIC 0x794c764f

    +struct ovl_config {
    + char *lowerdir;
    + char *upperdir;
    + char *workdir;
    +};
    +
    +/* private information held for overlayfs's superblock */
    struct ovl_fs {
    struct vfsmount *upper_mnt;
    struct vfsmount *lower_mnt;
    struct dentry *workdir;
    long lower_namelen;
    + /* pathnames of lower and upper dirs, for show_options */
    + struct ovl_config config;
    };

    +/* private information held for every overlayfs dentry */
    struct ovl_entry {
    /*
    * Keep "double reference" on upper dentries, so that
    @@ -373,6 +384,9 @@ static void ovl_put_super(struct super_block *sb)
    mntput(ufs->upper_mnt);
    mntput(ufs->lower_mnt);

    + kfree(ufs->config.lowerdir);
    + kfree(ufs->config.upperdir);
    + kfree(ufs->config.workdir);
    kfree(ufs);
    }

    @@ -421,16 +435,28 @@ static int ovl_statfs(struct dentry *dentry, struct kstatfs *buf)
    return err;
    }

    +/**
    + * ovl_show_options
    + *
    + * Prints the mount options for a given superblock.
    + * Returns zero; does not fail.
    + */
    +static int ovl_show_options(struct seq_file *m, struct dentry *dentry)
    +{
    + struct super_block *sb = dentry->d_sb;
    + struct ovl_fs *ufs = sb->s_fs_info;
    +
    + seq_printf(m, ",lowerdir=%s", ufs->config.lowerdir);
    + seq_printf(m, ",upperdir=%s", ufs->config.upperdir);
    + seq_printf(m, ",workdir=%s", ufs->config.workdir);
    + return 0;
    +}
    +
    static const struct super_operations ovl_super_operations = {
    .put_super = ovl_put_super,
    .remount_fs = ovl_remount_fs,
    .statfs = ovl_statfs,
    -};
    -
    -struct ovl_config {
    - char *lowerdir;
    - char *upperdir;
    - char *workdir;
    + .show_options = ovl_show_options,
    };

    enum {
    @@ -558,38 +584,38 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
    struct dentry *root_dentry;
    struct ovl_entry *oe;
    struct ovl_fs *ufs;
    - struct ovl_config config;
    struct kstatfs statfs;
    int err;

    - err = ovl_parse_opt((char *) data, &config);
    - if (err)
    + err = -ENOMEM;
    + ufs = kmalloc(sizeof(struct ovl_fs), GFP_KERNEL);
    + if (!ufs)
    goto out;

    + err = ovl_parse_opt((char *) data, &ufs->config);
    + if (err)
    + goto out_free_ufs;
    +
    err = -EINVAL;
    - if (!config.upperdir || !config.lowerdir || !config.workdir) {
    + if (!ufs->config.upperdir || !ufs->config.lowerdir ||
    + !ufs->config.workdir) {
    pr_err("overlayfs: missing upperdir or lowerdir or workdir\n");
    goto out_free_config;
    }

    - err = -ENOMEM;
    - ufs = kmalloc(sizeof(struct ovl_fs), GFP_KERNEL);
    - if (!ufs)
    - goto out_free_config;
    -
    oe = ovl_alloc_entry();
    if (oe == NULL)
    - goto out_free_ufs;
    + goto out_free_config;

    - err = ovl_mount_dir(config.upperdir, &upperpath);
    + err = ovl_mount_dir(ufs->config.upperdir, &upperpath);
    if (err)
    goto out_free_oe;

    - err = ovl_mount_dir(config.lowerdir, &lowerpath);
    + err = ovl_mount_dir(ufs->config.lowerdir, &lowerpath);
    if (err)
    goto out_put_upperpath;

    - err = ovl_mount_dir(config.workdir, &workpath);
    + err = ovl_mount_dir(ufs->config.workdir, &workpath);
    if (err)
    goto out_put_lowerpath;

    @@ -614,7 +640,7 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
    err = vfs_statfs(&lowerpath, &statfs);
    if (err) {
    pr_err("overlayfs: statfs failed on lowerpath\n");
    - goto out_put_lowerpath;
    + goto out_put_workpath;
    }
    ufs->lower_namelen = statfs.f_namelen;

    @@ -636,7 +662,7 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
    err = PTR_ERR(ufs->workdir);
    if (IS_ERR(ufs->workdir)) {
    pr_err("overlayfs: failed to create directory %s/%s\n",
    - config.workdir, OVL_WORKDIR_NAME);
    + ufs->config.workdir, OVL_WORKDIR_NAME);
    goto out_put_lower_mnt;
    }

    @@ -702,12 +728,12 @@ out_put_upperpath:
    path_put(&upperpath);
    out_free_oe:
    kfree(oe);
    +out_free_config:
    + kfree(ufs->config.lowerdir);
    + kfree(ufs->config.upperdir);
    + kfree(ufs->config.workdir);
    out_free_ufs:
    kfree(ufs);
    -out_free_config:
    - kfree(config.lowerdir);
    - kfree(config.upperdir);
    - kfree(config.workdir);
    out:
    return err;
    }
    --
    1.8.1.4


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