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Date: Tue, 19 Jul 2022 08:17:04 -0700
From: "Darrick J. Wong" <djwong@...nel.org>
To: Jeremy Bongio <bongiojp@...il.com>
Cc: Ted Tso <tytso@....edu>, linux-ext4@...r.kernel.org
Subject: Re: [PATCH v2] Add support for get/set UUID ioctls.
> Subject: [PATCH v2] Add support for get/set UUID ioctls.
Quick tip: Many people explicitly tag these userspace patches with the
name of the tool in the subject line, e.g.
[PATCH v2] tune2fs: add support for get/set UUID ioctls.
On Mon, Jul 18, 2022 at 11:56:37PM -0700, Jeremy Bongio wrote:
> When mounted, there is a race condition between changing the filesystem
> UUID and changing other aspects of the filesystem, like mounting, resizing,
> changing features, etc. Using these ioctls to get/set the UUID ensures the
> filesystem is not being resized.
>
> Signed-off-by: Jeremy Bongio <bongiojp@...il.com>
> ---
>
> fu_* fields are now named fsu_*.
>
> Removed EXT4_IOC_SETFSUUID_FLAG_BLOCKING flag.
>
> fsu_flags is initialized to 0.
>
> misc/tune2fs.c | 104 ++++++++++++++++++++++++++++++++++++++++---------
> 1 file changed, 86 insertions(+), 18 deletions(-)
>
> diff --git a/misc/tune2fs.c b/misc/tune2fs.c
> index 6c162ba5..39399d83 100644
> --- a/misc/tune2fs.c
> +++ b/misc/tune2fs.c
> @@ -82,11 +82,25 @@ extern int optind;
> #define FS_IOC_GETFSLABEL _IOR(0x94, 49, char[FSLABEL_MAX])
> #endif
>
> +struct fsuuid {
> + __u32 fsu_len;
> + __u32 fsu_flags;
> + __u8 fsu_uuid[];
> +};
> +
> +#ifndef EXT4_IOC_GETFSUUID
> +#define EXT4_IOC_GETFSUUID _IOR('f', 44, struct fsuuid)
> +#endif
> +
> +#ifndef EXT4_IOC_SETFSUUID
> +#define EXT4_IOC_SETFSUUID _IOW('f', 44, struct fsuuid)
> +#endif
> +
> extern int ask_yn(const char *string, int def);
>
> const char *program_name = "tune2fs";
> char *device_name;
> -char *new_label, *new_last_mounted, *new_UUID;
> +char *new_label, *new_last_mounted, *requested_uuid;
> char *io_options;
> static int c_flag, C_flag, e_flag, f_flag, g_flag, i_flag, l_flag, L_flag;
> static int m_flag, M_flag, Q_flag, r_flag, s_flag = -1, u_flag, U_flag, T_flag;
> @@ -2102,7 +2116,7 @@ static void parse_tune2fs_options(int argc, char **argv)
> open_flag = EXT2_FLAG_RW;
> break;
> case 'U':
> - new_UUID = optarg;
> + requested_uuid = optarg;
> U_flag = 1;
> open_flag = EXT2_FLAG_RW |
> EXT2_FLAG_JOURNAL_DEV_OK;
> @@ -3078,6 +3092,52 @@ int handle_fslabel(int setlabel) {
> return 0;
> }
>
> +/*
> + * Use EXT4_IOC_GETFSUUID/EXT4_IOC_SETFSUUID to get/set file system UUID.
> + * Return: 0 on success
> + * 1 on error
> + * -1 when the old method should be used
> + */
> +int handle_fsuuid(__u8 *uuid, bool get)
> +{
> + errcode_t ret;
> + int mnt_flags, fd;
> + char label[FSLABEL_MAX];
> + int maxlen = FSLABEL_MAX - 1;
> + char mntpt[PATH_MAX + 1];
> + struct fsuuid *fsuuid = NULL;
> +
> + fsuuid = malloc(sizeof(*fsuuid) + UUID_SIZE);
> + if (!fsuuid)
> + return -1;
> +
> + memcpy(fsuuid->fsu_uuid, uuid, UUID_SIZE);
> + fsuuid->fsu_len = UUID_SIZE;
> + fsuuid->fsu_flags = 0;
> +
> + ret = ext2fs_check_mount_point(device_name, &mnt_flags,
> + mntpt, sizeof(mntpt));
> + if (ret || !(mnt_flags & EXT2_MF_MOUNTED) ||
> + (!get && (mnt_flags & EXT2_MF_READONLY)) ||
> + !mntpt[0])
> + return -1;
> +
> + fd = open(mntpt, O_RDONLY);
> + if (fd < 0)
> + return -1;
> +
> + if (get) {
> + if (ioctl(fd, EXT4_IOC_GETFSUUID, fsuuid))
> + ret = -1;
> + } else {
> + if (ioctl(fd, EXT4_IOC_SETFSUUID, fsuuid))
> + ret = -1;
> + }
> + close(fd);
> + return ret;
ret is probably zero here, right?
That said, I don't think it's a great idea to go mixing errcode_t and
"the normal libc int return value" like that, since (a) that's type
confusion and (b)
return 0;
gets the point across with less effort.
> +}
> +
> +
> #ifndef BUILD_AS_LIB
> int main(int argc, char **argv)
> #else
> @@ -3454,6 +3514,7 @@ _("Warning: The journal is dirty. You may wish to replay the journal like:\n\n"
> dgrp_t i;
> char buf[SUPERBLOCK_SIZE] __attribute__ ((aligned(8)));
> __u8 old_uuid[UUID_SIZE];
> + uuid_t new_uuid;
>
> if (ext2fs_has_feature_stable_inodes(fs->super)) {
> fputs(_("Cannot change the UUID of this filesystem "
> @@ -3507,25 +3568,34 @@ _("Warning: The journal is dirty. You may wish to replay the journal like:\n\n"
> set_csum = 1;
> }
>
> - memcpy(old_uuid, sb->s_uuid, UUID_SIZE);
> - if ((strcasecmp(new_UUID, "null") == 0) ||
> - (strcasecmp(new_UUID, "clear") == 0)) {
> - uuid_clear(sb->s_uuid);
> - } else if (strcasecmp(new_UUID, "time") == 0) {
> - uuid_generate_time(sb->s_uuid);
> - } else if (strcasecmp(new_UUID, "random") == 0) {
> - uuid_generate(sb->s_uuid);
> - } else if (uuid_parse(new_UUID, sb->s_uuid)) {
> + rc = handle_fsuuid(old_uuid, true);
Might also be helpful to readers to wrap handle_fsuuid with something
containing "get" and "set" in the name explicitly, e.g.
static inline int get_mounted_fsuuid(__u8 *old_uuid)
{
return handle_fssuid(old_uuid, true);
}
I /think/ the rest looks plausible, but oof tune2fs is a bear to read.
My apologies for all the random cruft I've contributed over the years
(rewriting every inode on the filesystem to add checksums? seriously??)
--D
> + if (rc == -1)
> + memcpy(old_uuid, sb->s_uuid, UUID_SIZE);
> +
> + if ((strcasecmp(requested_uuid, "null") == 0) ||
> + (strcasecmp(requested_uuid, "clear") == 0)) {
> + uuid_clear(new_uuid);
> + } else if (strcasecmp(requested_uuid, "time") == 0) {
> + uuid_generate_time(new_uuid);
> + } else if (strcasecmp(requested_uuid, "random") == 0) {
> + uuid_generate(new_uuid);
> + } else if (uuid_parse(requested_uuid, new_uuid)) {
> com_err(program_name, 0, "%s",
> _("Invalid UUID format\n"));
> rc = 1;
> goto closefs;
> }
> - ext2fs_init_csum_seed(fs);
> - if (set_csum) {
> - for (i = 0; i < fs->group_desc_count; i++)
> - ext2fs_group_desc_csum_set(fs, i);
> - fs->flags &= ~EXT2_FLAG_SUPER_ONLY;
> +
> + rc = handle_fsuuid(new_uuid, false);
> + if (rc == -1) {
> + memcpy(sb->s_uuid, new_uuid, UUID_SIZE);
> + ext2fs_init_csum_seed(fs);
> + if (set_csum) {
> + for (i = 0; i < fs->group_desc_count; i++)
> + ext2fs_group_desc_csum_set(fs, i);
> + fs->flags &= ~EXT2_FLAG_SUPER_ONLY;
> + }
> + ext2fs_mark_super_dirty(fs);
> }
>
> /* If this is a journal dev, we need to copy UUID into jsb */
> @@ -3549,8 +3619,6 @@ _("Warning: The journal is dirty. You may wish to replay the journal like:\n\n"
> if ((rc = fs_update_journal_user(sb, old_uuid)))
> goto closefs;
> }
> -
> - ext2fs_mark_super_dirty(fs);
> }
>
> if (I_flag) {
> --
> 2.37.0.170.g444d1eabd0-goog
>
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