Re: [Qemu-trivial] [Qemu-devel] [PATCH v4] ivshmem: allow the sharing of mmap'd files

[Damien Millescamps <damien.millescamps@6wind.com>]

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On 09/20/2013 10:45 PM, Benoît Canet wrote:
> Le Friday 20 Sep 2013 à 20:34:47 (+0200), Damien Millescamps a écrit :
>> This patch permits to share memory areas that do not specifically belong to
>> /dev/shm. In such case, the file must be already present when launching qemu.
>> A new parameter 'file' has been added to specify the file to use.
>>
>> A use case for this patch is sharing huge pages available through a
>> hugetlbfs mountpoint.
>>
>> Signed-off-by: Damien Millescamps <damien.millescamps@6wind.com>
>> ---
>>  docs/specs/ivshmem_device_spec.txt |    7 +++-
>>  hw/misc/ivshmem.c                  |   56 +++++++++++++++++++++++------------
>>  2 files changed, 42 insertions(+), 21 deletions(-)
>>
>> diff --git a/docs/specs/ivshmem_device_spec.txt b/docs/specs/ivshmem_device_spec.txt
>> index 667a862..cb7d310 100644
>> --- a/docs/specs/ivshmem_device_spec.txt
>> +++ b/docs/specs/ivshmem_device_spec.txt
>> @@ -4,8 +4,11 @@ Device Specification for Inter-VM shared memory device
>>  
>>  The Inter-VM shared memory device is designed to share a region of memory to
>>  userspace in multiple virtual guests.  The memory region does not belong to any
>> -guest, but is a POSIX memory object on the host.  Optionally, the device may
>> -support sending interrupts to other guests sharing the same memory region.
>> +guest, but is a either a POSIX memory object or a mmap'd file (including
>> +hugepage-backed file) on the host.
>> +
>> +Optionally, the device may support sending interrupts to other guests sharing
>> +the same memory region.
>>  
>>  
>>  The Inter-VM PCI device
>> diff --git a/hw/misc/ivshmem.c b/hw/misc/ivshmem.c
>> index 2838866..5d991cf 100644
>> --- a/hw/misc/ivshmem.c
>> +++ b/hw/misc/ivshmem.c
>> @@ -98,6 +98,7 @@ typedef struct IVShmemState {
>>      Error *migration_blocker;
>>  
>>      char * shmobj;
>> +    char * fileobj;
>>      char * sizearg;
>>      char * role;
>>      int role_val;   /* scalar to avoid multiple string comparisons */
>> @@ -715,9 +716,10 @@ static int pci_ivshmem_init(PCIDevice *dev)
>>          /* if we get a UNIX socket as the parameter we will talk
>>           * to the ivshmem server to receive the memory region */
>>  
>> -        if (s->shmobj != NULL) {
>> -            fprintf(stderr, "WARNING: do not specify both 'chardev' "
>> -                                                "and 'shm' with ivshmem\n");
>> +        if (s->shmobj != NULL || s->fileobj != NULL) {
>> +            fprintf(stderr, "WARNING: both 'chardev' and '%s' specified.\n"
>> +                            "Falling back to 'chardev' only.\n",
>> +                            s->shmobj ? "shm" : "file");
>>          }
>>  
>>          IVSHMEM_DPRINTF("using shared memory server (socket = %s)\n",
>> @@ -743,28 +745,43 @@ static int pci_ivshmem_init(PCIDevice *dev)
>>      } else {
>>          /* just map the file immediately, we're not using a server */
>>          int fd;
>> +        int is_shm = !!(s->shmobj != NULL);
>> +        int is_file = !!(s->fileobj != NULL);
> Out of curiosity why doing !! on a boolean which would be converted either to
> zero or one by implicit casting ?
>
>>  
>> -        if (s->shmobj == NULL) {
>> -            fprintf(stderr, "Must specify 'chardev' or 'shm' to ivshmem\n");
>> +        if (!(is_shm ^ is_file)) {
>> +            fprintf(stderr, "ERROR: both 'file' and 'shm' specified for the "
>> +                            "same ivshmem device.\n");
>>              exit(1);
>>          }
>>  
>> -        IVSHMEM_DPRINTF("using shm_open (shm object = %s)\n", s->shmobj);
>> -
>> -        /* try opening with O_EXCL and if it succeeds zero the memory
>> -         * by truncating to 0 */
>> -        if ((fd = shm_open(s->shmobj, O_CREAT|O_RDWR|O_EXCL,
>> -                        S_IRWXU|S_IRWXG|S_IRWXO)) > 0) {
>> -           /* truncate file to length PCI device's memory */
>> -            if (ftruncate(fd, s->ivshmem_size) != 0) {
>> -                fprintf(stderr, "ivshmem: could not truncate shared file\n");
>> +        if (is_shm) {
>> +            IVSHMEM_DPRINTF("using shm_open (shm object = %s)\n", s->shmobj);
>> +
>> +            /* try opening with O_EXCL and if it succeeds zero the memory
>> +             * by truncating to 0 */
>> +            if ((fd = shm_open(s->shmobj, O_CREAT|O_RDWR|O_EXCL,
>> +                            S_IRWXU|S_IRWXG|S_IRWXO)) > 0) {
>> +               /* truncate file to length PCI device's memory */
>> +                if (ftruncate(fd, s->ivshmem_size) != 0) {
>> +                    fprintf(stderr, "ivshmem: could not truncate"
>> +                                    " shared file: %m\n");
>> +                    exit(-1);
>> +                }
>> +
>> +            } else if ((fd = shm_open(s->shmobj, O_RDWR,
>> +                            S_IRWXU|S_IRWXG|S_IRWXO)) < 0) {
>> +                fprintf(stderr, "ivshmem: could not open shared file: %m\n");
>> +                exit(-1);
>>              }
>> +        } else {
>> +            IVSHMEM_DPRINTF("using open (file object = %s)\n", s->fileobj);
>>  
>> -        } else if ((fd = shm_open(s->shmobj, O_CREAT|O_RDWR,
>> -                        S_IRWXU|S_IRWXG|S_IRWXO)) < 0) {
>> -            fprintf(stderr, "ivshmem: could not open shared file\n");
>> -            exit(-1);
>> -
>> +            /* try opening a mmap's file. This file must have been previously
>> +             * created on the host */
>> +            if ((fd = open(s->fileobj, O_RDWR)) < 0) {
>> +                fprintf(stderr, "ivshmem: could not open mmap'd file: %m\n");
>> +                exit(-1);
>> +            }
>>          }
>>  
>>          if (check_shm_size(s, fd) == -1) {
>> @@ -804,6 +821,7 @@ static Property ivshmem_properties[] = {
>>      DEFINE_PROP_BIT("ioeventfd", IVShmemState, features, IVSHMEM_IOEVENTFD, false),
>>      DEFINE_PROP_BIT("msi", IVShmemState, features, IVSHMEM_MSI, true),
>>      DEFINE_PROP_STRING("shm", IVShmemState, shmobj),
>> +    DEFINE_PROP_STRING("file", IVShmemState, fileobj),
>>      DEFINE_PROP_STRING("role", IVShmemState, role),
>>      DEFINE_PROP_UINT32("use64", IVShmemState, ivshmem_64bit, 1),
>>      DEFINE_PROP_END_OF_LIST(),
>> -- 
>> 1.7.2.5
>>
>>
> Hi,
>
> I won't be able to help you much on the semantic of the patch.
> However you should ./script/checkpatch.pl before posting:
>
> benoit@Laure:~/qemu (quorum_reboot2)$ ./scripts/checkpatch.pl /tmp/onx 
> ERROR: "foo * bar" should be "foo *bar"
> #115: FILE: hw/misc/ivshmem.c:101:
> +    char * fileobj;
>
> WARNING: suspect code indent for conditional statements (12, 15)
> #162: FILE: hw/misc/ivshmem.c:762:
> +            if ((fd = shm_open(s->shmobj, O_CREAT|O_RDWR|O_EXCL,
> [...]
> +               /* truncate file to length PCI device's memory */
>
> ERROR: do not use assignment in if condition
> #162: FILE: hw/misc/ivshmem.c:762:
> +            if ((fd = shm_open(s->shmobj, O_CREAT|O_RDWR|O_EXCL,
>
> ERROR: do not use assignment in if condition
> #171: FILE: hw/misc/ivshmem.c:771:
> +            } else if ((fd = shm_open(s->shmobj, O_RDWR,
>
> ERROR: do not use assignment in if condition
> #186: FILE: hw/misc/ivshmem.c:781:
> +            if ((fd = open(s->fileobj, O_RDWR)) < 0) {
>
> total: 4 errors, 1 warnings, 99 lines checked
>
> /tmp/patch has style problems, please review.  If any of these errors
> are false positives report them to the maintainer, see
> CHECKPATCH in MAINTAINERS.
>
> Best regards
>
> Benoît
Well, I am actually a bit confused by the rule:
*Follow the coding style* and run /scripts/checkpatch.pl <patchfile>/
before submitting.
from the submit patch guidelines, since I assume that the coding style
is referring to the file coding style ?

The whole file might need a complete clean up, but I understand that it
should be in a separate patch from this rule, since the whole file is
written like that:
*Don't include irrelevant changes*. In particular, don't include
formatting, coding style or whitespace changes to bits of code that
would otherwise not be touched by the patch.

This is a just an indentation modification to put it inside a if/else...

Cheers,
-- 
Damien


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