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    Subject[PATCH 4/4] parse options in the vfs level
    Date
    This patch introduces a simple generic vfs option parser.
    Right now, the only option we have is to limit the size of the dcache.

    So any user that wants to have a dcache entries limit, can specify:

    mount -o whatever_options,vfs_dcache_size=XXX <dev> <mntpoint>

    It is supposed to work well with remounts, allowing it to change
    multiple over the course of the filesystem's lifecycle.

    I find mount a natural interface for handling filesystem options,
    so that's what I've choosen. Feel free to yell at it at will if
    you disagree.

    Signed-off-by: Glauber Costa <glommer@parallels.com>
    CC: Dave Chinner <david@fromorbit.com>
    ---
    fs/namespace.c | 89 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
    1 files changed, 89 insertions(+), 0 deletions(-)

    diff --git a/fs/namespace.c b/fs/namespace.c
    index 22bfe82..11ce45d 100644
    --- a/fs/namespace.c
    +++ b/fs/namespace.c
    @@ -31,6 +31,7 @@
    #include <linux/idr.h>
    #include <linux/fs_struct.h>
    #include <linux/fsnotify.h>
    +#include <linux/parser.h>
    #include <asm/uaccess.h>
    #include <asm/unistd.h>
    #include "pnode.h"
    @@ -2271,6 +2272,82 @@ int copy_mount_string(const void __user *data, char **where)
    return 0;
    }

    +static const match_table_t tokens = {
    + {1, "vfs_dcache_size=%u"},
    +};
    +
    +struct vfs_options {
    + unsigned long vfs_dcache_size;
    +};
    +
    +/**
    + * Generic option parsing for the VFS.
    + *
    + * Since most of the filesystems already do their own option parsing, and with
    + * very few code shared between them, this function strips out any options that
    + * we succeed in parsing ourselves. Passing them forward would just give the
    + * underlying fs an option it does not expect, leading it to fail.
    + *
    + * We don't yet have a pointer to the super block as well, since this is
    + * pre-mount. We accumulate in struct vfs_options whatever data we collected,
    + * and act on it later.
    + */
    +static int vfs_parse_options(char *options, struct vfs_options *ops)
    +{
    + substring_t args[MAX_OPT_ARGS];
    + unsigned int option;
    + char *p;
    + char *opt;
    + char *start = NULL;
    + int ret;
    +
    + if (!options)
    + return 0;
    +
    + opt = kstrdup(options, GFP_KERNEL);
    + if (!opt)
    + return 1;
    +
    + ret = 1;
    +
    + start = opt;
    + while ((p = strsep(&opt, ",")) != NULL) {
    + int token;
    + if (!*p)
    + continue;
    +
    + /*
    + * Initialize args struct so we know whether arg was
    + * found; some options take optional arguments.
    + */
    + args[0].to = args[0].from = 0;
    + token = match_token(p, tokens, args);
    + switch (token) {
    + case 1:
    + if (!args[0].from)
    + break;
    +
    + if (match_int(&args[0], &option))
    + break;
    + else
    + ops->vfs_dcache_size = option;
    +
    + ret = 0;
    + if (!opt) /* it is the last option listed */
    + *(options + (p - start)) = '\0';
    + else
    + strcpy(options + (p - start), opt);
    + break;
    + default:
    + ret = 0;
    + break;
    + }
    + }
    +
    + kfree(start);
    + return ret;
    +}
    +
    /*
    * Flags is a 32-bit value that allows up to 31 non-fs dependent flags to
    * be given to the mount() call (ie: read-only, no-dev, no-suid etc).
    @@ -2291,6 +2368,7 @@ long do_mount(char *dev_name, char *dir_name, char *type_page,
    struct path path;
    int retval = 0;
    int mnt_flags = 0;
    + struct vfs_options vfs_options;

    /* Discard magic */
    if ((flags & MS_MGC_MSK) == MS_MGC_VAL)
    @@ -2318,6 +2396,12 @@ long do_mount(char *dev_name, char *dir_name, char *type_page,
    if (!(flags & MS_NOATIME))
    mnt_flags |= MNT_RELATIME;

    +
    + vfs_options.vfs_dcache_size = INT_MAX;
    + retval = vfs_parse_options(data_page, &vfs_options);
    + if (retval)
    + goto dput_out;
    +
    /* Separate the per-mountpoint flags */
    if (flags & MS_NOSUID)
    mnt_flags |= MNT_NOSUID;
    @@ -2350,6 +2434,11 @@ long do_mount(char *dev_name, char *dir_name, char *type_page,
    else
    retval = do_new_mount(&path, type_page, flags, mnt_flags,
    dev_name, data_page);
    +
    + if (!retval)
    + vfs_set_dcache_size(path.mnt->mnt_sb,
    + vfs_options.vfs_dcache_size);
    +
    dput_out:
    path_put(&path);
    return retval;
    --
    1.7.6


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