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erjo@1087
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1 Allow to boot on any directories in a filesystem. You will be able to :
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2 - have several distributions in one partition
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3 - use efficently the disk space between several distributions
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4 - deduplicate files across several distributions
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5 - test new configurations
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6 ...
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7 The bad news : you can't remount /
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8
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erjo@1087
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9 --- linux-3.2.53/Documentation/kernel-parameters.txt
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10 +++ linux-3.2.53/Documentation/kernel-parameters.txt
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11 @@ -2324,8 +2324,9 @@
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12
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13 ro [KNL] Mount root device read-only on boot
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14
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15 - root= [KNL] Root filesystem
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16 + root= [KNL] Root filesystem and root directory
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17 See name_to_dev_t comment in init/do_mounts.c.
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18 + Format: <root_filesystem>[:root_directory]
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19
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20 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
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21 mount the root filesystem
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erjo@1087
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22 --- linux-3.2.40/init/do_mounts.c
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23 +++ linux-3.2.40/init/do_mounts.c
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24 @@ -28,6 +28,7 @@
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25 int root_mountflags = MS_RDONLY | MS_SILENT;
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erjo@1087
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26 static char * __initdata root_device_name;
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erjo@1087
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27 static char __initdata saved_root_name[64];
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28 +static char __initdata saved_root_directory[256];
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29 static int root_wait;
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30
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31 dev_t ROOT_DEV;
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32 @@ -255,7 +256,20 @@
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33
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34 static int __init root_dev_setup(char *line)
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35 {
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36 + char *s;
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37 +
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38 + strcpy(saved_root_directory, ".");
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erjo@1087
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39 strlcpy(saved_root_name, line, sizeof(saved_root_name));
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erjo@1087
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40 + s = strchr(saved_root_name, ':');
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41 + if (s) {
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erjo@1087
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42 + *s = '\0';
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erjo@1087
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43 + s = strchr(line, ':');
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erjo@1087
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44 + for (s++; *s == '/'; s++);
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erjo@1087
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45 + if (*s) {
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erjo@1087
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46 + strlcpy(saved_root_directory, s,
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47 + sizeof(saved_root_directory));
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erjo@1087
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48 + }
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erjo@1087
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49 + }
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erjo@1087
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50 return 1;
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erjo@1087
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51 }
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52
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53 @@ -554,5 +568,5 @@
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54 out:
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55 devtmpfs_mount("dev");
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56 sys_mount(".", "/", NULL, MS_MOVE, NULL);
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57 - sys_chroot((const char __user __force *)".");
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58 + sys_chroot((const char __user __force *)saved_root_directory);
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erjo@1087
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59 }
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