basebuilder_pel7ppc64bebuilder0
7 years ago
1 changed files with 159 additions and 0 deletions
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From 2218dc0d130bb72809e2d8b26a36402bf6293727 Mon Sep 17 00:00:00 2001 |
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From: Karel Zak <kzak@redhat.com> |
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Date: Mon, 17 Aug 2015 11:54:26 +0200 |
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Subject: [PATCH 84/86] libmount: add support for "bind,ro" |
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Now it's necessary to use two mount(8) calls to create a read-only |
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mount: |
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mount /foo /bar -o bind |
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mount /bar -o remount,ro,bind |
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This patch allows to specify "bind,ro" and the remount is done |
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automatically by libmount by additional mount(2) syscall. It's not |
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atomic of course. |
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Addresses: http://bugzilla.redhat.com/show_bug.cgi?id=1281839 |
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Signed-off-by: Karel Zak <kzak@redhat.com> |
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--- |
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libmount/src/context_mount.c | 46 ++++++++++++++++++++++++++++++++++++++++++++ |
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sys-utils/mount.8 | 37 ++++++++++++++++++----------------- |
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2 files changed, 65 insertions(+), 18 deletions(-) |
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diff --git a/libmount/src/context_mount.c b/libmount/src/context_mount.c |
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index d6691eb..4df2646 100644 |
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--- a/libmount/src/context_mount.c |
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+++ b/libmount/src/context_mount.c |
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@@ -62,6 +62,10 @@ static int mnt_context_append_additional_mount(struct libmnt_context *cxt, |
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return 0; |
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} |
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+/* |
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+ * add additional mount(2) syscall requests when necessary to set propagation flags |
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+ * after regular mount(2). |
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+ */ |
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static int init_propagation(struct libmnt_context *cxt) |
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{ |
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char *name; |
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@@ -102,6 +106,41 @@ static int init_propagation(struct libmnt_context *cxt) |
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} |
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/* |
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+ * add additional mount(2) syscall request to implement "ro,bind", the first regular |
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+ * mount(2) is the "bind" operation, the second is "remount,ro,bind" call. |
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+ * |
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+ * Note that we don't remove "ro" from the first syscall (kernel silently |
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+ * ignores this flags for bind operation) -- maybe one day kernel will support |
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+ * read-only binds in one step and then all will be done by the firts mount(2) and the |
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+ * second remount will be noop... |
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+ */ |
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+static int init_robind(struct libmnt_context *cxt) |
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+{ |
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+ struct libmnt_addmount *ad; |
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+ int rc; |
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+ |
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+ assert(cxt); |
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+ assert(cxt->mountflags & MS_BIND); |
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+ assert(cxt->mountflags & MS_RDONLY); |
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+ assert(!(cxt->mountflags & MS_REMOUNT)); |
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+ |
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+ DBG(CXT, mnt_debug_h(cxt, "mount: initialize additional ro,bind mount")); |
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+ |
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+ ad = mnt_new_addmount(); |
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+ if (!ad) |
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+ return -ENOMEM; |
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+ |
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+ ad->mountflags = MS_REMOUNT | MS_BIND | MS_RDONLY; |
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+ if (cxt->mountflags & MS_REC) |
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+ ad->mountflags |= MS_REC; |
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+ rc = mnt_context_append_additional_mount(cxt, ad); |
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+ if (rc) |
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+ return rc; |
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+ |
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+ return 0; |
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+} |
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+ |
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+/* |
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* this has to be called after mnt_context_evaluate_permissions() |
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*/ |
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static int fix_optstr(struct libmnt_context *cxt) |
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@@ -174,6 +213,13 @@ static int fix_optstr(struct libmnt_context *cxt) |
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if (rc) |
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return rc; |
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} |
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+ if ((cxt->mountflags & MS_BIND) |
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+ && (cxt->mountflags & MS_RDONLY) |
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+ && !(cxt->mountflags & MS_REMOUNT)) { |
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+ rc = init_robind(cxt); |
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+ if (rc) |
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+ return rc; |
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+ } |
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next = fs->fs_optstr; |
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diff --git a/sys-utils/mount.8 b/sys-utils/mount.8 |
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index 3648870..49cb281 100644 |
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--- a/sys-utils/mount.8 |
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+++ b/sys-utils/mount.8 |
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@@ -388,25 +388,25 @@ or shortoption |
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.\" available since Linux 2.4.11. |
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Note that the filesystem mount options will remain the same as those |
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-on the original mount point, and cannot be changed by passing the -o |
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-option along with --bind/--rbind. The mount options can be |
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-changed by a separate remount command, for example: |
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+on the original mount point. |
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+ |
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+.BR mount(8) |
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+since v2.27 (backported to RHEL7.3) allow to change the options by passing the |
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+.B \-o |
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+option along with |
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+.BR \-\-bind |
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+for example: |
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.RS |
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.br |
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-.B mount --bind |
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-.I olddir newdir |
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-.br |
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-.B mount -o remount,ro |
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-.I newdir |
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+.B mount \-\-bind,ro foo foo |
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.RE |
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-Note that behavior of the remount operation depends on the /etc/mtab file. The |
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-first command stores the 'bind' flag to the /etc/mtab file and the second |
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-command reads the flag from the file. If you have a system without the |
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-/etc/mtab file or if you explicitly define source and target for the remount |
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-command (then mount(8) does not read /etc/mtab), then you have to use bind flag |
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-(or option) for the remount command too. For example: |
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+This feature is not supported by Linux kernel and it is implemented in userspace |
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+by additional remount mount(2) syscall. This solution is not atomic. |
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+ |
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+The alternative (classic) way to create a read-only bind mount is to use remount |
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+operation, for example: |
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.RS |
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.br |
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@@ -417,14 +417,15 @@ command (then mount(8) does not read /etc/mtab), then you have to use bind flag |
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.I olddir newdir |
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.RE |
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-Note that |
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-.I remount,ro,bind |
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-will create a read-only mountpoint (VFS entry), but the original filesystem suberblock |
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-will be still writable, it means that the |
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+Note that read-only bind will create a read-only mountpoint (VFS entry), but the |
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+original filesystem superblock will still be writable, meaning that the |
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.I olddir |
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will be writable, but the |
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.I newdir |
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will be read-only. |
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+ |
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+It's impossible to change mount options recursively |
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+(for example with \fB -o rbind,ro\fR). |
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.RE |
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.B The move operation. |
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-- |
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2.7.4 |
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