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

[GN Keshava <keshava.gn@gmail.com>]

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)?
Considering option #2, How I can find device path programatically from my C
file?

Thanks again for the help. :)
With regards,
Keshava

On Tue, 27 Sep 2016 at 15:19 Laszlo Ersek <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>> 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
> >
>
>