On 21.03.2011 19:17, Colin Watson wrote:
> This would make it easier to use grub-fstest to inspect files in
> filesystems supported by GRUB without needing to mount the device. The
> same thing can be done using the cp subcommand, but that requires a
> temporary file which often isn't needed. A cat subcommand is generally
> more convenient.
>
Patch is ok after 1.99.
> For context: temporarily mounting filesystems in the context of an OS
> installer or a tool such as os-prober can be problematic on Linux. In
> particular, if you want to inspect files on a journalled filesystem,
> then you have three choices to the best of my knowledge:
>
> 1) Just go ahead and mount it read-only. This seems superficially
> sensible. Unfortunately, Linux's journalling filesystem
> implementations will write to the block device anyway. If the
> filesystem was hibernated, disaster will ensue. (And, on
> principle, the kinds of places where I'm doing this kind of
> read-only mount, such as os-prober, should never write to the
> disk.)
>
> 2) Mark the block device read-only using blockdev, to ensure that even
> journalling filesystems will never write to it. This solves the
> hibernation problem, but has two other flaws. If the journal needs
> recovery, mounting will fail when an ordinary read-only mount would
> succeed; and blockdev has system-wide effect, so this will
> interfere with anything unlucky enough to be trying to mount the
> filesystem for real at the same time.
>
> 3) Create a device-mapper snapshot of the block device and operate on
> that. Unfortunately, if the block device is not itself a
> device-mapper device, this increments the reference count of the
> block device such that you can't mount the filesystem on it
> ("/dev/foo already mounted or /mnt busy").
>
> I'm thus getting increasingly tempted to use grub-fstest for this kind
> of application wherever possible. Of course we need a fallback for
> architectures where GRUB doesn't yet work, but aside from that I suspect
> that it would make things significantly more reliable.
>
> 2011-03-21 Colin Watson <cjwat...@ubuntu.com>
>
> * util/grub-fstest.c (cmd_cat): New function.
> (fstest): Handle CMD_CAT.
> (options): Add cat.
> (argp_parser): Handle cat.
>
> === modified file 'util/grub-fstest.c'
> --- util/grub-fstest.c 2010-09-20 18:09:31 +0000
> +++ util/grub-fstest.c 2011-03-21 17:32:32 +0000
> @@ -54,12 +54,15 @@ execute_command (char *name, int n, char
> return (cmd->func) (cmd, n, args);
> }
>
> -#define CMD_LS 1
> -#define CMD_CP 2
> -#define CMD_CMP 3
> -#define CMD_HEX 4
> -#define CMD_CRC 6
> -#define CMD_BLOCKLIST 7
> +enum {
> + CMD_LS = 1,
> + CMD_CP,
> + CMD_CAT,
> + CMD_CMP,
> + CMD_HEX,
> + CMD_CRC,
> + CMD_BLOCKLIST
> +};
>
> #define BUF_SIZE 32256
>
> @@ -182,6 +185,26 @@ cmd_cp (char *src, char *dest)
> }
>
> static void
> +cmd_cat (char *src)
> +{
> + auto int cat_hook (grub_off_t ofs, char *buf, int len);
> + int cat_hook (grub_off_t ofs, char *buf, int len)
> + {
> + (void) ofs;
> +
> + if ((int) fwrite (buf, 1, len, stdout) != len)
> + {
> + grub_util_error (_("write error"));
> + return 1;
> + }
> +
> + return 0;
> + }
> +
> + read_file (src, cat_hook);
> +}
> +
> +static void
> cmd_cmp (char *src, char *dest)
> {
> FILE *ff;
> @@ -312,6 +335,9 @@ fstest (int n, char **args)
> case CMD_CP:
> cmd_cp (args[0], args[1]);
> break;
> + case CMD_CAT:
> + cmd_cat (args[0]);
> + break;
> case CMD_CMP:
> cmd_cmp (args[0], args[1]);
> break;
> @@ -347,6 +373,7 @@ static struct argp_option options[] = {
> {0, 0, 0 , OPTION_DOC, N_("Commands:"), 1},
> {N_("ls PATH"), 0, 0 , OPTION_DOC, N_("List files in PATH."), 1},
> {N_("cp FILE LOCAL"), 0, 0, OPTION_DOC, N_("Copy FILE to local file
> LOCAL."), 1},
> + {N_("cat FILE"), 0, 0 , OPTION_DOC, N_("Copy FILE to standard
> output."), 1},
> {N_("cmp FILE LOCAL"), 0, 0, OPTION_DOC, N_("Compare FILE with local file
> LOCAL."), 1},
> {N_("hex FILE"), 0, 0 , OPTION_DOC, N_("Hex dump FILE."), 1},
> {N_("crc FILE"), 0, 0 , OPTION_DOC, N_("Get crc32 checksum of FILE."),
> 1},
> @@ -459,6 +486,11 @@ argp_parser (int key, char *arg, struct
> cmd = CMD_CP;
> nparm = 2;
> }
> + else if (!grub_strcmp (arg, "cat"))
> + {
> + cmd = CMD_CAT;
> + nparm = 1;
> + }
> else if (!grub_strcmp (arg, "cmp"))
> {
> cmd = CMD_CMP;
>
> -- Regards Vladimir 'φ-coder/phcoder' Serbinenko
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