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

[Laszlo Ersek <lersek@redhat.com>]

On 09/27/16 17:07, Carsey, Jaben wrote:
> Apparently all the good threads happen at night for me...

The blessings of a distributed team! ;)

> Kesheva,
> 
> There are a few functions in the ShellLib that call into the UEFI Shell binary to help you. Some of these are duplicates of what others suggested, but I figured I would elaborate.

I appreciate that, thanks!

Cheers,
Laszlo

> ShellOpenFileMetaArg - open a file or group of files.  can handle something like "open *.txt"
> ShellOpenFileByName - open a single file.
> 
> These functions in turn call into functions in the ShellProtocol that the UEFI Shell produces during the time it is running.
> 
> ShellOpenFileMetaArg  calls into gEfiShellProtocol->OpenFileList
> ShellOpenFileByName  calls into gEfiShellProtocol->OpenFileByName
> 
> There is some examples of use of these functions in the files for the commands "Touch" and "Type" and these are located in: ShellPkg\Library\UefiShellLevel3CommandsLib
> 
> 
> -Jaben
> 
>> -----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 <lersek@redhat.com>
>> Cc: edk2-devel@lists.01.org <edk2-devel@ml01.01.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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