Libguestfs - Nov 2022 - [p2v PATCH] disks.c: skip SCSI floppy drives with no disk inserted

A SCSI floppy drive with no disk inserted looks like a normal /dev/sd*
node, but causes the nbdkit file plugin to fail with ENOMEDIUM. Filter out
such devices altogether -- unlike CD-ROMs (for which we create a device
model in the target, albeit with no medium inserted), empty floppies
should not be converted in any way.

https://bugzilla.redhat.com/show_bug.cgi?id=2140997
Signed-off-by: Laszlo Ersek <lersek at redhat.com>
---

Notes:
    This patch still needs testing; the ISO image is at
   
<http://lacos.interhost.hu/exclude-floppies-rhbz-2140997/b19895a5acd1/livecd-p2v-202211091434.iso>,
    sha256 sum:
    b0666a9140b03e12829982179bf7da2ac5477737fb53760d2e8c527d8a2bf55a.

 disks.c | 58 ++++++++++++++++++++
 1 file changed, 58 insertions(+)

diff --git a/disks.c b/disks.c
index 4eb006246d84..aafe467f9e9a 100644
--- a/disks.c
+++ b/disks.c
@@ -20,6 +20,7 @@
 #include <dirent.h>
 #include <errno.h>
 #include <error.h>
+#include <fcntl.h>
 #include <inttypes.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -67,6 +68,57 @@ partition_parent (dev_t part_dev)
   return makedev (parent_major, parent_minor);
 }
 
+/**
+ * Return true if the named device (eg. C<dev == "sda">) is a
Removable Media
+ * SCSI Disk with no media inserted. This covers floppy drives, but not CD-ROM
+ * drives (intentionally).
+ */
+static int
+device_has_no_media (const char *dev)
+{
+  int ret;
+  gchar *sysfs_pathname;
+  gchar *sysfs_contents;
+  gsize sysfs_size;
+  gchar *dev_pathname;
+  int dev_fd;
+
+  ret = 0;
+
+  if (!STRPREFIX (dev, "sd"))
+    return ret;
+
+  sysfs_pathname = g_strdup_printf ("/sys/block/%s/removable", dev);
+
+  if (!g_file_get_contents (sysfs_pathname, &sysfs_contents,
&sysfs_size, NULL))
+    goto free_sysfs_pathname;
+
+  if (sysfs_size < 2 || sysfs_contents[0] != '1' ||
sysfs_contents[1] != '\n')
+    goto free_sysfs_contents;
+
+  dev_pathname = g_strdup_printf ("/dev/%s", dev);
+
+  dev_fd = open (dev_pathname, O_RDONLY | O_CLOEXEC);
+  if (dev_fd == -1) {
+    if (errno == ENOMEDIUM)
+      ret = 1;
+
+    goto free_dev_pathname;
+  }
+  close (dev_fd);
+
+free_dev_pathname:
+  g_free (dev_pathname);
+
+free_sysfs_contents:
+  g_free (sysfs_contents);
+
+free_sysfs_pathname:
+  g_free (sysfs_pathname);
+
+  return ret;
+}
+
 /**
  * Return true if the named device (eg. C<dev == "sda">)
contains the
  * root filesystem.  C<root_device> is the major:minor of the root
@@ -139,6 +191,12 @@ find_all_disks (char ***disks, char ***removable)
         STRPREFIX (d->d_name, "ubd") ||
         STRPREFIX (d->d_name, "vd")) {
       char *p;
+      /* Skip SCSI disk drives with removable media that have no media inserted
+       * -- effectively, empty floppy drives. Note that SCSI CD-ROMs are named
+       * C<sr*> and thus handled on the other branch.
+       */
+      if (device_has_no_media (d->d_name))
+        continue;
 
       /* Skip the device containing the root filesystem. */
       if (device_contains (d->d_name, root_device))

Hi Rich,

On 11/09/22 14:52, Laszlo Ersek wrote:
> A SCSI floppy drive with no disk inserted looks like a normal /dev/sd*
> node, but causes the nbdkit file plugin to fail with ENOMEDIUM. Filter out
> such devices altogether -- unlike CD-ROMs (for which we create a device
> model in the target, albeit with no medium inserted), empty floppies
> should not be converted in any way.
> 
> https://bugzilla.redhat.com/show_bug.cgi?id=2140997
> Signed-off-by: Laszlo Ersek <lersek at redhat.com>
> ---
> 
> Notes:
>     This patch still needs testing; the ISO image is at
>    
<http://lacos.interhost.hu/exclude-floppies-rhbz-2140997/b19895a5acd1/livecd-p2v-202211091434.iso>,
>     sha256 sum:
>     b0666a9140b03e12829982179bf7da2ac5477737fb53760d2e8c527d8a2bf55a.
> 
>  disks.c | 58 ++++++++++++++++++++
>  1 file changed, 58 insertions(+)
> 
> diff --git a/disks.c b/disks.c
> index 4eb006246d84..aafe467f9e9a 100644
> --- a/disks.c
> +++ b/disks.c
> @@ -20,6 +20,7 @@
>  #include <dirent.h>
>  #include <errno.h>
>  #include <error.h>
> +#include <fcntl.h>
>  #include <inttypes.h>
>  #include <stdio.h>
>  #include <stdlib.h>
> @@ -67,6 +68,57 @@ partition_parent (dev_t part_dev)
>    return makedev (parent_major, parent_minor);
>  }
>  
> +/**
> + * Return true if the named device (eg. C<dev == "sda">)
is a Removable Media
> + * SCSI Disk with no media inserted. This covers floppy drives, but not
CD-ROM
> + * drives (intentionally).
> + */
> +static int
> +device_has_no_media (const char *dev)
> +{
> +  int ret;
> +  gchar *sysfs_pathname;
> +  gchar *sysfs_contents;
> +  gsize sysfs_size;
> +  gchar *dev_pathname;
> +  int dev_fd;
> +
> +  ret = 0;
> +
> +  if (!STRPREFIX (dev, "sd"))
> +    return ret;
> +
> +  sysfs_pathname = g_strdup_printf ("/sys/block/%s/removable",
dev);
> +
> +  if (!g_file_get_contents (sysfs_pathname, &sysfs_contents,
&sysfs_size, NULL))
> +    goto free_sysfs_pathname;
> +
> +  if (sysfs_size < 2 || sysfs_contents[0] != '1' ||
sysfs_contents[1] != '\n')
> +    goto free_sysfs_contents;
> +
> +  dev_pathname = g_strdup_printf ("/dev/%s", dev);
> +
> +  dev_fd = open (dev_pathname, O_RDONLY | O_CLOEXEC);
> +  if (dev_fd == -1) {
> +    if (errno == ENOMEDIUM)
> +      ret = 1;
> +
> +    goto free_dev_pathname;
> +  }
> +  close (dev_fd);
> +
> +free_dev_pathname:
> +  g_free (dev_pathname);
> +
> +free_sysfs_contents:
> +  g_free (sysfs_contents);
> +
> +free_sysfs_pathname:
> +  g_free (sysfs_pathname);
> +
> +  return ret;
> +}
> +
>  /**
>   * Return true if the named device (eg. C<dev == "sda">)
contains the
>   * root filesystem.  C<root_device> is the major:minor of the root
> @@ -139,6 +191,12 @@ find_all_disks (char ***disks, char ***removable)
>          STRPREFIX (d->d_name, "ubd") ||
>          STRPREFIX (d->d_name, "vd")) {
>        char *p;
> +      /* Skip SCSI disk drives with removable media that have no media
inserted
> +       * -- effectively, empty floppy drives. Note that SCSI CD-ROMs are
named
> +       * C<sr*> and thus handled on the other branch.
> +       */
> +      if (device_has_no_media (d->d_name))
> +        continue;
>  
>        /* Skip the device containing the root filesystem. */
>        if (device_contains (d->d_name, root_device))
> _______________________________________________
> Libguestfs mailing list
> Libguestfs at redhat.com
> https://listman.redhat.com/mailman/listinfo/libguestfs
> 
Tingting and Vera have verified this patch, in
<https://bugzilla.redhat.com/show_bug.cgi?id=2140997>. Are you OK with
the patch? (Sorry for asking if it has been on your radar already!)

Thanks,
Laszlo