[LTP] [PATCH] tst_find_backing_dev: Get dev name from /sys/dev/block/*/uevent

[Alessandro Carminati]

Hello,

Thank you this new version of the patch.
in this moment doc/c-test-api.txt is out of sync with the code, I can
handle its fix.

Regards
Alessandro

On Tue, Oct 25, 2022, 16:59 Richard Palethorpe <rpalethorpe@suse.com> wrote:

> mountinfo doesn't always contain the correct device name. For example
> /dev/root may be displayed, but not exist in devtmpfs[1].
>
> The unevent file in sysfs is another way of finding the device name
> from the major and minor numbers. Possibly it always displays the
> proper device name.
>
> One caveat is the sysfs can be disabled, so this commit does not
> remove the mountinfo method altogether, but leaves it as a fallback.
>
> Alessandro Carminati originally sent two patches[1] which added the
> uevent file method as a fallback. However it seems like the better
> method.
>
> [1]: https://lore.kernel.org/ltp/Y0023HcAOlhfAcJw@lab.hqhome163.com/
>
> Signed-off-by: Richard Palethorpe <rpalethorpe@suse.com>
> Suggested-by: Alessandro Carminati <alessandro.carminati@gmail.com>
> Reported-by: Alessandro Carminati <alessandro.carminati@gmail.com>
> ---
>
> Alessandro, it seems you tried to edit the last patch by hand? In any
> case it did not apply and I ended up making some other changes. So I
> took the liberty of submitting a new patch.
>
> Thanks,
> Richard.
>
>  lib/tst_device.c | 20 ++++++++++++++++++--
>  1 file changed, 18 insertions(+), 2 deletions(-)
>
> diff --git a/lib/tst_device.c b/lib/tst_device.c
> index 8419b80c3..676903fff 100644
> --- a/lib/tst_device.c
> +++ b/lib/tst_device.c
> @@ -526,14 +526,30 @@ void tst_find_backing_dev(const char *path, char
> *dev)
>         unsigned int dev_major, dev_minor, line_mjr, line_mnr;
>         unsigned int len, best_match_len = 1;
>         char mnt_point[PATH_MAX];
> +       char uevent_path[PATH_MAX];
> +       char dev_name[NAME_MAX];
>
>         if (stat(path, &buf) < 0)
>                 tst_brkm(TWARN | TERRNO, NULL, "stat() failed");
>
> +       *dev = '\0';
>         dev_major = major(buf.st_dev);
>         dev_minor = minor(buf.st_dev);
> +
> +       sprintf(uevent_path,
> +               "/sys/dev/block/%d:%d/uevent", dev_major, dev_minor);
> +
> +       if (!access(uevent_path, R_OK)) {
> +               FILE_LINES_SCANF(NULL, uevent_path, "DEVNAME=%s",
> dev_name);
> +
> +               if (dev_name[0])
> +                       sprintf(dev, "/dev/%s", dev_name);
> +       }
> +
> +       if (!stat(dev, &buf))
> +               goto out;
> +
>         file = SAFE_FOPEN(NULL, "/proc/self/mountinfo", "r");
> -       *dev = '\0';
>
>         while (fgets(line, sizeof(line), file)) {
>                 if (sscanf(line, "%*d %*d %d:%d %*s %s",
> @@ -564,7 +580,7 @@ void tst_find_backing_dev(const char *path, char *dev)
>
>         if (stat(dev, &buf) < 0)
>                 tst_brkm(TWARN | TERRNO, NULL, "stat(%s) failed", dev);
> -
> +out:
>         if (S_ISBLK(buf.st_mode) != 1)
>                 tst_brkm(TCONF, NULL, "dev(%s) isn't a block dev", dev);
>  }
> --
> 2.36.1
>
>
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