[syslinux] [PATCH] : Add diskbypartname option to chain.c32

[poma]

On 15.07.2016 03:50, Ady Ady via Syslinux wrote:
> Looking at the UEFI specs, and _if_ I understand Erwan's patch correctly, 
> we are talking about searching for a "Partition Name". Avoiding the 
> "label" term for this new option should help in reducing some potential 
> confusions (e.g. BSD's "disklabel", fdisk's "partition label (type)", 
> filesystem's "volume label"...).
> 
> So, IMO, "diskbypartname" should be a reasonable contraction of "disk 
> being selected by searching for a GPT Partition Name".
> 
> If it has not been clear enough in prior emails, this new 
> "diskbypartname" option could be applicable for users with a 
> (Protective) MBR in a GPT scheme booting in BIOS / CSM mode.
> 
> I am basing this patch on Syslinux 6.04-pre1. At the time of writing 
> this email, it is also equivalent to basing it on the current git 
> master head.
> 
> If the patch is accepted, it would be helpful for users to also see 
> 'doc/chain.txt' being patched. Additional potential rewording in 
> 'com32/chain/{chain.c,options.c} might be helpful too in future 
> separated patches.
> 
> I took Erwan's patch and slightly modified it with some rewording and 
> by changing "dlabel" to "diskbypartname". I hope I've done it 
> correctly; please evaluate it with careful attention. I have not 
> compiled any binaries with this patch.
> 
> The following is the relevant text for the patch and the patching code 
> for 'com32/chain/chain.c' and for 'com32/chain/options.c.
> 
> 
> 
> 
> The existing "label:" and "guid:" options select a specified partition 
> and jump to it.
> 
> The new "diskbypartname" option searches in disks for a GPT partition 
> with the specified Partition Name, and jumps to the first _disk_ that 
> matches the search.
> 
> The specified partition might not be related to the boot process; its 
> Name is just used for the detection / selection of the disk.
> 
> A possible use case is for making a localboot like:
> 
>     label localboot
>         com32 chain.c32
>         append diskbypartname=datapartition
> 
> This option allows booting a disk that contains at least one GPT 
> partition named "datapartition".
> 
> The "diskbypartname:" option can be considered as doing almost what the 
> "mbr:" option does, but by searching for a specified Partition Name in 
> the GPT partitions.
> 
> 
> diff U3 syslinux-6.04-pre1/com32/chain/chain.c diskbypartname/com32/chain/chain.c
> --- syslinux-6.04-pre1/com32/chain/chain.c	Fri Jul 15 01:27:23 2016
> +++ diskbypartname/com32/chain/chain.c	Fri Jul 15 01:00:03 2016
> @@ -143,6 +143,38 @@
>      return drive;
>  }
>  
> +/*
> + * Search for a disk having a GPT partition with a specified Partition Name.
> + * Return disk and iterator at proper position.
> + */
> +static int find_disk_by_partition_name(const char *label, struct part_iter **_boot_part)
> +{
> +    struct part_iter *iter = NULL;
> +    struct disk_info diskinfo;
> +    int drive;
> +
> +    for (drive = 0x80; drive < 0x80 + fixed_cnt; drive++) {
> +	if (disk_get_params(drive, &diskinfo))
> +	    continue;		/* Drive doesn't exist */
> +	if (!(iter = pi_begin(&diskinfo, opt.piflags)))
> +	    continue;
> +	/* Check for a matching GPT Partition Name */
> +	if (iter->type == typegpt)
> +	    while (!pi_next(iter)) {
> +		if (!strcmp(label, iter->gpt.part_label))
> +		    // We don't care about the actual partition that matched
> +		    pi_del(&iter);
> +		    // Let's return the disk itself instead
> +		    iter = pi_begin(&diskinfo, opt.piflags);
> +		    goto ok;
> +	    }
> +    }
> +    drive = -1;
> +ok:
> +    *_boot_part = iter;
> +    return drive;
> +}
> +
>  static void do_boot(struct data_area *data, int ndata)
>  {
>      struct syslinux_memmap *mmap;
> @@ -300,6 +332,15 @@
>  	}
>  	if (find_by_label(opt.drivename + 6, &iter) < 0) {
>  	    error("Unable to find requested GPT partition by label.");
> +	    goto bail;
> +	}
> +    } else if (!strncmp(opt.drivename, "diskbypartname", 14)) {
> +	if (!opt.drivename[15]) {
> +	    error("No partition name specified.");
> +	    goto bail;
> +	}
> +	if (find_disk_by_partition_name(opt.drivename + 15, &iter) < 0) {
> +	    error("Unable to find requested GPT partition by name.");
>  	    goto bail;
>  	}
>      } else if ((opt.drivename[0] == 'h' || opt.drivename[0] == 'f') &&
> 
> 
> 
> diff U3 syslinux-6.04-pre1/com32/chain/options.c diskbypartname/com32/chain/options.c
> --- syslinux-6.04-pre1/com32/chain/options.c	Fri Jul 15 01:28:29 2016
> +++ diskbypartname/com32/chain/options.c	Fri Jul 15 00:56:26 2016
> @@ -107,6 +107,7 @@
>  "  direct partition selection:",
>  "        chain.c32 guid=<guid> [options]",
>  "        chain.c32 label=<label> [options]",
> +"        chain.c32 diskbypartname=<partition_name> [options]",
>  "        chain.c32 fs [options]",
>  "",
>  "You can use ':' instead of '=' and ' ' instead of ','.",
> @@ -396,6 +397,8 @@
>  		   || !strncmp(argv[i], "guid=", 5)
>  		   || !strncmp(argv[i], "label:", 6)
>  		   || !strncmp(argv[i], "label=", 6)
> +		   || !strncmp(argv[i], "diskbypartname:", 15)
> +		   || !strncmp(argv[i], "diskbypartname=", 15)
>  		   || !strcmp(argv[i], "boot")
>  		   || !strncmp(argv[i], "boot,", 5)
>  		   || !strcmp(argv[i], "fs")) {
> 
>  --
> 
> 

dlabel -> diskbypartname
+1