diff mbox series

[1/1] diskpart: lock the device before writing the disklabel

Message ID 20210704150937.46996-1-james.hilliard1@gmail.com
State Accepted
Headers show
Series [1/1] diskpart: lock the device before writing the disklabel | expand

Commit Message

James Hilliard July 4, 2021, 3:09 p.m. UTC 
This should help make sure it is safe to modify the disk
before we modify the partition table.

Adapted from:
https://github.com/karelzak/util-linux/blob/v2.37/lib/blkdev.c#L365-L413

Signed-off-by: James Hilliard <james.hilliard1@gmail.com>
---
 handlers/diskpart_handler.c | 35 +++++++++++++++++++++++++++++++++--
 1 file changed, 33 insertions(+), 2 deletions(-)

Comments

James Hilliard July 20, 2021, 3:40 p.m. UTC | #1 
On Sun, Jul 4, 2021 at 9:09 AM James Hilliard <james.hilliard1@gmail.com> wrote:
>
> This should help make sure it is safe to modify the disk
> before we modify the partition table.

FYI this appears to be required for systemd-udevd interoperability, see:
https://systemd.io/BLOCK_DEVICE_LOCKING/

>
> Adapted from:
> https://github.com/karelzak/util-linux/blob/v2.37/lib/blkdev.c#L365-L413
>
> Signed-off-by: James Hilliard <james.hilliard1@gmail.com>
> ---
>  handlers/diskpart_handler.c | 35 +++++++++++++++++++++++++++++++++--
>  1 file changed, 33 insertions(+), 2 deletions(-)
>
> diff --git a/handlers/diskpart_handler.c b/handlers/diskpart_handler.c
> index 5eba2bd..09832ec 100644
> --- a/handlers/diskpart_handler.c
> +++ b/handlers/diskpart_handler.c
> @@ -13,6 +13,7 @@
>  #include <string.h>
>  #include <errno.h>
>  #include <ctype.h>
> +#include <sys/file.h>
>  #include <sys/types.h>
>  #include <libfdisk/libfdisk.h>
>  #include "swupdate.h"
> @@ -634,14 +635,44 @@ static int diskpart_compare_tables(struct diskpart_table *tb, struct diskpart_ta
>         return ret;
>  }
>
> +static int diskpart_blkdev_lock(struct fdisk_context *cxt)
> +{
> +       int oper = LOCK_EX;
> +       int ret = 0;
> +
> +       if (fdisk_device_is_used(cxt)) {
> +               ERROR("%s: device is in use", fdisk_get_devname(cxt));
> +               return -EBUSY;
> +       }
> +
> +       if (!fdisk_is_readonly(cxt)) {
> +               ret = flock(fdisk_get_devfd(cxt), oper);
> +               if (ret) {
> +                       switch (errno) {
> +                               case EWOULDBLOCK:
> +                                       ERROR("%s: device already locked", fdisk_get_devname(cxt));
> +                                       break;
> +                               default:
> +                                       ERROR("%s: failed to get lock", fdisk_get_devname(cxt));
> +                       }
> +                       return -EBUSY;
> +               }
> +       }
> +       return ret;
> +}
> +
>  static int diskpart_write_table(struct fdisk_context *cxt, struct create_table *createtable)
>  {
>         int ret = 0;
>
> -       if (createtable->parent || createtable->child)
> +       if (createtable->parent || createtable->child) {
>                 TRACE("Partitions on disk differ, write to disk;");
> -       else
> +               ret = diskpart_blkdev_lock(PARENT(cxt));
> +               if (ret)
> +                       return ret;
> +       } else {
>                 TRACE("Same partition table on disk, do not touch partition table !");
> +       }
>
>         if (createtable->child) {
>                 if (!IS_HYBRID(cxt)) {
> --
> 2.32.0
>
Stefano Babic July 21, 2021, 12:19 p.m. UTC | #2 
Hi James,

On 04.07.21 17:09, James Hilliard wrote:
> This should help make sure it is safe to modify the disk
> before we modify the partition table.
> 
> Adapted from:
> https://github.com/karelzak/util-linux/blob/v2.37/lib/blkdev.c#L365-L413
> 
> Signed-off-by: James Hilliard <james.hilliard1@gmail.com>
> ---
>   handlers/diskpart_handler.c | 35 +++++++++++++++++++++++++++++++++--
>   1 file changed, 33 insertions(+), 2 deletions(-)
> 
> diff --git a/handlers/diskpart_handler.c b/handlers/diskpart_handler.c
> index 5eba2bd..09832ec 100644
> --- a/handlers/diskpart_handler.c
> +++ b/handlers/diskpart_handler.c
> @@ -13,6 +13,7 @@
>   #include <string.h>
>   #include <errno.h>
>   #include <ctype.h>
> +#include <sys/file.h>
>   #include <sys/types.h>
>   #include <libfdisk/libfdisk.h>
>   #include "swupdate.h"
> @@ -634,14 +635,44 @@ static int diskpart_compare_tables(struct diskpart_table *tb, struct diskpart_ta
>   	return ret;
>   }
>   
> +static int diskpart_blkdev_lock(struct fdisk_context *cxt)
> +{
> +	int oper = LOCK_EX;
> +	int ret = 0;
> +
> +	if (fdisk_device_is_used(cxt)) {
> +		ERROR("%s: device is in use", fdisk_get_devname(cxt));
> +		return -EBUSY;
> +	}
> +
> +	if (!fdisk_is_readonly(cxt)) {
> +		ret = flock(fdisk_get_devfd(cxt), oper);
> +		if (ret) {
> +			switch (errno) {
> +				case EWOULDBLOCK:
> +					ERROR("%s: device already locked", fdisk_get_devname(cxt));
> +					break;
> +				default:
> +					ERROR("%s: failed to get lock", fdisk_get_devname(cxt));
> +			}
> +			return -EBUSY;
> +		}
> +	}
> +	return ret;
> +}
> +
>   static int diskpart_write_table(struct fdisk_context *cxt, struct create_table *createtable)
>   {
>   	int ret = 0;
>   
> -	if (createtable->parent || createtable->child)
> +	if (createtable->parent || createtable->child) {
>   		TRACE("Partitions on disk differ, write to disk;");
> -	else
> +		ret = diskpart_blkdev_lock(PARENT(cxt));
> +		if (ret)
> +			return ret;
> +	} else {
>   		TRACE("Same partition table on disk, do not touch partition table !");
> +	}
>   
>   	if (createtable->child) {
>   		if (!IS_HYBRID(cxt)) {
> 

I am missing how the lock is release, that is, where the file descriptor 
is implicitely closed by fdisk ? I will be sure that if I run SWUpdate 
twice without rebooting still works.

Regards,
Stefano
James Hilliard July 21, 2021, 1:55 p.m. UTC | #3 
On Wed, Jul 21, 2021 at 6:19 AM Stefano Babic <sbabic@denx.de> wrote:
>
> Hi James,
>
> On 04.07.21 17:09, James Hilliard wrote:
> > This should help make sure it is safe to modify the disk
> > before we modify the partition table.
> >
> > Adapted from:
> > https://github.com/karelzak/util-linux/blob/v2.37/lib/blkdev.c#L365-L413
> >
> > Signed-off-by: James Hilliard <james.hilliard1@gmail.com>
> > ---
> >   handlers/diskpart_handler.c | 35 +++++++++++++++++++++++++++++++++--
> >   1 file changed, 33 insertions(+), 2 deletions(-)
> >
> > diff --git a/handlers/diskpart_handler.c b/handlers/diskpart_handler.c
> > index 5eba2bd..09832ec 100644
> > --- a/handlers/diskpart_handler.c
> > +++ b/handlers/diskpart_handler.c
> > @@ -13,6 +13,7 @@
> >   #include <string.h>
> >   #include <errno.h>
> >   #include <ctype.h>
> > +#include <sys/file.h>
> >   #include <sys/types.h>
> >   #include <libfdisk/libfdisk.h>
> >   #include "swupdate.h"
> > @@ -634,14 +635,44 @@ static int diskpart_compare_tables(struct diskpart_table *tb, struct diskpart_ta
> >       return ret;
> >   }
> >
> > +static int diskpart_blkdev_lock(struct fdisk_context *cxt)
> > +{
> > +     int oper = LOCK_EX;
> > +     int ret = 0;
> > +
> > +     if (fdisk_device_is_used(cxt)) {
> > +             ERROR("%s: device is in use", fdisk_get_devname(cxt));
> > +             return -EBUSY;
> > +     }
> > +
> > +     if (!fdisk_is_readonly(cxt)) {
> > +             ret = flock(fdisk_get_devfd(cxt), oper);
> > +             if (ret) {
> > +                     switch (errno) {
> > +                             case EWOULDBLOCK:
> > +                                     ERROR("%s: device already locked", fdisk_get_devname(cxt));
> > +                                     break;
> > +                             default:
> > +                                     ERROR("%s: failed to get lock", fdisk_get_devname(cxt));
> > +                     }
> > +                     return -EBUSY;
> > +             }
> > +     }
> > +     return ret;
> > +}
> > +
> >   static int diskpart_write_table(struct fdisk_context *cxt, struct create_table *createtable)
> >   {
> >       int ret = 0;
> >
> > -     if (createtable->parent || createtable->child)
> > +     if (createtable->parent || createtable->child) {
> >               TRACE("Partitions on disk differ, write to disk;");
> > -     else
> > +             ret = diskpart_blkdev_lock(PARENT(cxt));
> > +             if (ret)
> > +                     return ret;
> > +     } else {
> >               TRACE("Same partition table on disk, do not touch partition table !");
> > +     }
> >
> >       if (createtable->child) {
> >               if (!IS_HYBRID(cxt)) {
> >
>
> I am missing how the lock is release, that is, where the file descriptor
> is implicitely closed by fdisk ? I will be sure that if I run SWUpdate
> twice without rebooting still works.

I think it's here:
https://github.com/karelzak/util-linux/blob/v2.37/libfdisk/src/context.c#L770

Which gets called from here:
https://github.com/sbabic/swupdate/blob/eb8657fa91754029e4cd16df3e959a3498779599/handlers/diskpart_handler.c#L896

>
> Regards,
> Stefano
>
> --
> =====================================================================
> DENX Software Engineering GmbH,      Managing Director: Wolfgang Denk
> HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
> Phone: +49-8142-66989-53 Fax: +49-8142-66989-80 Email: sbabic@denx.de
> =====================================================================
Stefano Babic July 21, 2021, 2:34 p.m. UTC | #4 
Hi James,

On 21.07.21 15:55, James Hilliard wrote:
> On Wed, Jul 21, 2021 at 6:19 AM Stefano Babic <sbabic@denx.de> wrote:
>>
>> Hi James,
>>
>> On 04.07.21 17:09, James Hilliard wrote:
>>> This should help make sure it is safe to modify the disk
>>> before we modify the partition table.
>>>
>>> Adapted from:
>>> https://github.com/karelzak/util-linux/blob/v2.37/lib/blkdev.c#L365-L413
>>>
>>> Signed-off-by: James Hilliard <james.hilliard1@gmail.com>
>>> ---
>>>    handlers/diskpart_handler.c | 35 +++++++++++++++++++++++++++++++++--
>>>    1 file changed, 33 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/handlers/diskpart_handler.c b/handlers/diskpart_handler.c
>>> index 5eba2bd..09832ec 100644
>>> --- a/handlers/diskpart_handler.c
>>> +++ b/handlers/diskpart_handler.c
>>> @@ -13,6 +13,7 @@
>>>    #include <string.h>
>>>    #include <errno.h>
>>>    #include <ctype.h>
>>> +#include <sys/file.h>
>>>    #include <sys/types.h>
>>>    #include <libfdisk/libfdisk.h>
>>>    #include "swupdate.h"
>>> @@ -634,14 +635,44 @@ static int diskpart_compare_tables(struct diskpart_table *tb, struct diskpart_ta
>>>        return ret;
>>>    }
>>>
>>> +static int diskpart_blkdev_lock(struct fdisk_context *cxt)
>>> +{
>>> +     int oper = LOCK_EX;
>>> +     int ret = 0;
>>> +
>>> +     if (fdisk_device_is_used(cxt)) {
>>> +             ERROR("%s: device is in use", fdisk_get_devname(cxt));
>>> +             return -EBUSY;
>>> +     }
>>> +
>>> +     if (!fdisk_is_readonly(cxt)) {
>>> +             ret = flock(fdisk_get_devfd(cxt), oper);
>>> +             if (ret) {
>>> +                     switch (errno) {
>>> +                             case EWOULDBLOCK:
>>> +                                     ERROR("%s: device already locked", fdisk_get_devname(cxt));
>>> +                                     break;
>>> +                             default:
>>> +                                     ERROR("%s: failed to get lock", fdisk_get_devname(cxt));
>>> +                     }
>>> +                     return -EBUSY;
>>> +             }
>>> +     }
>>> +     return ret;
>>> +}
>>> +
>>>    static int diskpart_write_table(struct fdisk_context *cxt, struct create_table *createtable)
>>>    {
>>>        int ret = 0;
>>>
>>> -     if (createtable->parent || createtable->child)
>>> +     if (createtable->parent || createtable->child) {
>>>                TRACE("Partitions on disk differ, write to disk;");
>>> -     else
>>> +             ret = diskpart_blkdev_lock(PARENT(cxt));
>>> +             if (ret)
>>> +                     return ret;
>>> +     } else {
>>>                TRACE("Same partition table on disk, do not touch partition table !");
>>> +     }
>>>
>>>        if (createtable->child) {
>>>                if (!IS_HYBRID(cxt)) {
>>>
>>
>> I am missing how the lock is release, that is, where the file descriptor
>> is implicitely closed by fdisk ? I will be sure that if I run SWUpdate
>> twice without rebooting still works.
> 
> I think it's here:
> https://github.com/karelzak/util-linux/blob/v2.37/libfdisk/src/context.c#L770
> 
> Which gets called from here:
> https://github.com/sbabic/swupdate/blob/eb8657fa91754029e4cd16df3e959a3498779599/handlers/diskpart_handler.c#L896
> 

Ah ok, thanks ! That's fine, I will just test on a device and apply the 
patch.

Regards,
Stefano
diff mbox series

Patch

diff --git a/handlers/diskpart_handler.c b/handlers/diskpart_handler.c
index 5eba2bd..09832ec 100644
--- a/handlers/diskpart_handler.c
+++ b/handlers/diskpart_handler.c
@@ -13,6 +13,7 @@ 
 #include <string.h>
 #include <errno.h>
 #include <ctype.h>
+#include <sys/file.h>
 #include <sys/types.h>
 #include <libfdisk/libfdisk.h>
 #include "swupdate.h"
@@ -634,14 +635,44 @@  static int diskpart_compare_tables(struct diskpart_table *tb, struct diskpart_ta
 	return ret;
 }
 
+static int diskpart_blkdev_lock(struct fdisk_context *cxt)
+{
+	int oper = LOCK_EX;
+	int ret = 0;
+
+	if (fdisk_device_is_used(cxt)) {
+		ERROR("%s: device is in use", fdisk_get_devname(cxt));
+		return -EBUSY;
+	}
+
+	if (!fdisk_is_readonly(cxt)) {
+		ret = flock(fdisk_get_devfd(cxt), oper);
+		if (ret) {
+			switch (errno) {
+				case EWOULDBLOCK:
+					ERROR("%s: device already locked", fdisk_get_devname(cxt));
+					break;
+				default:
+					ERROR("%s: failed to get lock", fdisk_get_devname(cxt));
+			}
+			return -EBUSY;
+		}
+	}
+	return ret;
+}
+
 static int diskpart_write_table(struct fdisk_context *cxt, struct create_table *createtable)
 {
 	int ret = 0;
 
-	if (createtable->parent || createtable->child)
+	if (createtable->parent || createtable->child) {
 		TRACE("Partitions on disk differ, write to disk;");
-	else
+		ret = diskpart_blkdev_lock(PARENT(cxt));
+		if (ret)
+			return ret;
+	} else {
 		TRACE("Same partition table on disk, do not touch partition table !");
+	}
 
 	if (createtable->child) {
 		if (!IS_HYBRID(cxt)) {