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To: GN Keshava <keshava.gn@gmail.com>
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From: Laszlo Ersek <lersek@redhat.com>
Cc: "edk2-devel@lists.01.org" <edk2-devel@ml01.01.org>
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Date: Tue, 27 Sep 2016 11:16:20 +0200
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Subject: Re: How to open a file by it's full path in UEFI
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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