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    Subject[PATCH] init: Support mounting devices from kernel command line
    Date
    This patch adds support to mounting devices using a kernel parameter.

    Such feature is usefull for virtual guests. It allows easily automating
    mounts without having to change the base image (which can be read-only).

    In /tools/kvm we are interested in such feature to allow us to automatically
    mount user home directory using virtio-9p from the host to the guest
    filesystem under '/hostfs'.

    Cc: Avi Kivity <avi@redhat.com>
    Cc: Ingo Molnar <mingo@elte.hu>
    Cc: Pekka Enberg <penberg@kernel.org>
    Signed-off-by: Sasha Levin <levinsasha928@gmail.com>
    ---
    Documentation/kernel-parameters.txt | 6 +++
    init/do_mounts.c | 61 +++++++++++++++++++++++++++++++++++
    2 files changed, 67 insertions(+), 0 deletions(-)

    diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
    index aa47be7..e1955fb 100644
    --- a/Documentation/kernel-parameters.txt
    +++ b/Documentation/kernel-parameters.txt
    @@ -1476,6 +1476,12 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
    log everything. Information is printed at KERN_DEBUG
    so loglevel=8 may also need to be specified.

    + mount=
    + [KNL] Mount a device to a mount point after loading
    + rootfs and setting up devices. Can be used to mount
    + up to 16 devices.
    + Format: <source>,<destination>,<fs>[,<params>]
    +
    mousedev.tap_time=
    [MOUSE] Maximum time between finger touching and
    leaving touchpad surface for touch to be considered
    diff --git a/init/do_mounts.c b/init/do_mounts.c
    index c0851a8..0948f1d 100644
    --- a/init/do_mounts.c
    +++ b/init/do_mounts.c
    @@ -29,9 +29,24 @@ int root_mountflags = MS_RDONLY | MS_SILENT;
    static char * __initdata root_device_name;
    static char __initdata saved_root_name[64];
    static int __initdata root_wait;
    +static char * __initdata user_mount[16];
    +static int __initdata user_mount_count;

    dev_t ROOT_DEV;

    +static int __init setup_user_mount(char *str)
    +{
    + if (user_mount_count > 15) {
    + printk(KERN_ERR "More than 16 'mount=' options specified.")
    + return 1;
    + }
    +
    + user_mount[user_mount_count++] = str;
    +
    + return 1;
    +}
    +__setup("mount=", setup_user_mount);
    +
    static int __init load_ramdisk(char *str)
    {
    rd_doload = simple_strtol(str,NULL,0) & 3;
    @@ -431,6 +446,51 @@ void __init mount_root(void)
    #endif
    }

    +int __init do_user_mounts(void)
    +{
    + int i, res;
    + char *src, *dst, *fs, *params, *cur;
    +
    + for (i = 0; i < user_mount_count; i++) {
    + src = user_mount[i];
    + cur = strstr(user_mount[i], ",");
    + if (!cur)
    + goto fail_str;
    +
    + *cur = '\0';
    + dst = ++cur;
    +
    + cur = strstr(cur, ",");
    + if (!cur)
    + goto fail_str;
    +
    + *cur = '\0';
    + fs = ++cur;
    +
    + cur = strstr(cur, ",");
    + if (cur) {
    + *cur = '\0';
    + params = ++cur;
    + } else {
    + params = NULL;
    + }
    +
    + res = sys_mount(src, dst, fs, 0, params);
    + if (res == 0)
    + printk(KERN_INFO "Mounted (%s filesystem) %s to %s\n",
    + fs, src, dst);
    + else
    + printk(KERN_ERR "Failed mounting (%s filesystem) %s to"
    + " %s. Err: %d\n", fs, src, dst, res);
    + }
    +
    + return 0;
    +
    +fail_str:
    + printk(KERN_ERR "Bad mount str: %s\n", user_mount[i]);
    + return -1;
    +}
    +
    /*
    * Prepare the namespace - decide what/where to mount, load ramdisks, etc.
    */
    @@ -490,4 +550,5 @@ out:
    devtmpfs_mount("dev");
    sys_mount(".", "/", NULL, MS_MOVE, NULL);
    sys_chroot((const char __user __force *)".");
    + do_user_mounts();
    }
    --
    1.7.6


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