Re: How to open a file by it's full path in UEFI

[Andrew Fish <afish@apple.com>]

I was kind of surprised that an example like this did not exist in: https://github.com/tianocore/edk2/tree/master/ShellPkg/Application

Thanks,

Andrew Fish

> On Sep 27, 2016, at 9:44 AM, Jarlstrom, Laurie <laurie.jarlstrom@intel.com> wrote:
> 
> Keshava,
> Attached Sample code  is an example that will open a file name passed through the command line using the Shell.
> 
> 
> thanks,
> Laurie
>  
> laurie.jarlstrom@intel.com
> 
> Intel SSG/STO/EBP
> (503) 712-9395
> 
> 
> 
> -----Original Message-----
> From: edk2-devel [mailto:edk2-devel-bounces@lists.01.org] On Behalf Of GN Keshava
> Sent: Tuesday, September 27, 2016 4:52 AM
> To: Laszlo Ersek
> Cc: edk2-devel@lists.01.org
> Subject: Re: [edk2] How to open a file by it's full path in UEFI
> 
> Thank you Laszlo.
> 
> I'll check it out. :)
> 
> Thanks again.
> Regards,
> Keshava
> 
> On Tue, 27 Sep 2016 at 16:47 Laszlo Ersek <lersek@redhat.com> wrote:
> 
>> On 09/27/16 12:46, GN Keshava wrote:
>>> Hi Laszlo,
>>> 
>>> Thank you for the answer. It was helpful.
>>> 
>>> Considering option #1, can you give some more details (a small 
>>> example or any reference link would be helpful), how I can use Shell 
>>> APIs in my C file (which will compile to my .efi app)?
>> 
>> Hmmm, I don't have hands-on experience with this, but you might want 
>> to try the ShellOpenFileByName() function, from 
>> "ShellPkg/Include/Library/ShellLib.h".
>> 
>> You can find examples for UEFI applications that use the Shell library
>> with:
>> 
>>  git grep -w ShellLib -- '*inf'
>> 
>> or just grep the tree for ShellOpenFileByName().
>> 
>> See also "AppPkg/ReadMe.txt".
>> 
>>> Considering option #2, How I can find device path programatically 
>>> from my C file?
>> 
>> The EFI_SHELL_PROTOCOL.GetDevicePathFromMap() member function seems 
>> relevant -- it is specified in the UEFI Shell spec --, but I would 
>> definitely try ShellOpenFileByName() first.
>> 
>> Thanks
>> Laszlo
>> 
>>> Thanks again for the help. :)
>>> With regards,
>>> Keshava
>>> 
>>> On Tue, 27 Sep 2016 at 15:19 Laszlo Ersek <lersek@redhat.com 
>>> <mailto:lersek@redhat.com>> wrote:
>>> 
>>>    On 09/27/16 11:25, GN Keshava wrote:
>>>> Hi Laszlo,
>>>> 
>>>> Thanks for the reply. I meant I have complete file path. I 
>>> believe
>> the
>>>> "device path" is different. Is it possible to obtain DevicePath
>>>    using my
>>>> full file path?
>>> 
>>>    The pathname you seem to have (as "complete") is specific to a given
>>>    simple FS, so system-wide it cannot be considered complete 
>>> (there
>> can be
>>>    multiple filesystems).
>>> 
>>>    In your original email I missed that you started with "FS1:".
>> Andrew's
>>>    answer covers that case.
>>> 
>>>    In summary, you can do three things:
>>>    - have a pathname that starts with FSx: (which is a shell-specific
>>>    mapping), and use Andrew's recommendation,
>>>    - have a complete UEFI device path, and then use what I recommended,
>>>    - have no information for selecting the filesystem (from the many
>>>    possible), and use your current iteration.
>>> 
>>>    Options #1 and #2 actually correspond to each other, considering
>>>    "expressive power" / information content (as long as you are in the
>>>    shell); please see the MAP shell command.
>>> 
>>>    Thanks
>>>    Laszlo
>>> 
>>>> On Tue, 27 Sep 2016 at 14:46 Laszlo Ersek <lersek@redhat.com
>>>    <mailto:lersek@redhat.com>
>>>> <mailto:lersek@redhat.com <mailto:lersek@redhat.com>>> wrote:
>>>> 
>>>>    On 09/27/16 11:03, GN Keshava wrote:
>>>>> Hi all,
>>>>> 
>>>>> 
>>>>> I'm trying to open a file from my UEFI application. The path
>> of
>>>>    file is
>>>>> 
>>>>> fs1:/myfolder/myfile.txt
>>>>> 
>>>>> The code :
>>>>> 
>>>>> efiStatus = bs->LocateHandleBuffer(ByProtocol,
>>>>>                                   &sfspGuid,
>>>>>                                   NULL,
>>>>>                                   &handleCount,
>>>>>                                   &handles);
>>>>> 
>>>>> for (index = 0; index < (int)handleCount; ++ index)
>>>>> {
>>>>>    EFI_SIMPLE_FILE_SYSTEM_PROTOCOL* fs = NULL;
>>>>> 
>>>>>    efiStatus = bs->HandleProtocol(
>>>>>        handles[index],
>>>>>        &sfspGuid,
>>>>>        (void**)&fs);
>>>>> 
>>>>>    EFI_FILE_PROTOCOL* root = NULL;
>>>>>    ...
>>>>>    efiStatus = fs->OpenVolume(fs, &root);
>>>>> 
>>>>>    EFI_FILE_PROTOCOL* token = NULL;
>>>>> 
>>>>>    efiStatus = root->Open(
>>>>>        root,
>>>>>        &token,
>>>>>        L"myfolder\\myfile.txt",
>>>>>        EFI_FILE_MODE_READ,
>>>>>        EFI_FILE_READ_ONLY | EFI_FILE_HIDDEN |
>> EFI_FILE_SYSTEM);
>>>>> }
>>>>> 
>>>>> But using this method, I can only go through all the file
>> system
>>>>    handles
>>>>> and open each volume and try opening my file.
>>>>> 
>>>>> But I want to give full path to my file and open it in it's
>>>    volume.
>>>>> 
>>>>> How can I acheive this?
>>>>> Thanks.
>>>> 
>>>>    If you have a complete device path, you can use
>>>    gBS->LocateDevicePath()
>>>>    with gEfiSimpleFileSystemProtocolGuid, to locate the handle
>>>    with the
>>>>    most specific device path (--> the longest device path prefix)
>>>    with the
>>>>    simple FS protocol installed on it. Then you can check if the
>>>    remaining
>>>>    device path (returned by the service) consist of nothing but
>>>    one File
>>>>    Path Media Device Path node. If so, you can open the simple FS
>>>    protocol
>>>>    on the handle found, then use that to open the file by
>> pathname.
>>>> 
>>>>    Laszlo
>>>> 
>>> 
>> 
>> 
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