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Subject[PATCH 4/4] parse options in the vfs level
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This patch introduces a simple generic vfs option parser.
Right now, the only option we have is to limit the size of the dcache.

So any user that wants to have a dcache entries limit, can specify:

mount -o whatever_options,vfs_dcache_size=XXX <dev> <mntpoint>

It is supposed to work well with remounts, allowing it to change
multiple over the course of the filesystem's lifecycle.

I find mount a natural interface for handling filesystem options,
so that's what I've choosen. Feel free to yell at it at will if
you disagree.

Signed-off-by: Glauber Costa <glommer@parallels.com>
CC: Dave Chinner <david@fromorbit.com>
---
fs/namespace.c | 89 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
1 files changed, 89 insertions(+), 0 deletions(-)
diff --git a/fs/namespace.c b/fs/namespace.c
index 22bfe82..11ce45d 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -31,6 +31,7 @@
#include <linux/idr.h>
#include <linux/fs_struct.h>
#include <linux/fsnotify.h>
+#include <linux/parser.h>
#include <asm/uaccess.h>
#include <asm/unistd.h>
#include "pnode.h"
@@ -2271,6 +2272,82 @@ int copy_mount_string(const void __user *data, char **where)
return 0;
}

+static const match_table_t tokens = {
+ {1, "vfs_dcache_size=%u"},
+};
+
+struct vfs_options {
+ unsigned long vfs_dcache_size;
+};
+
+/**
+ * Generic option parsing for the VFS.
+ *
+ * Since most of the filesystems already do their own option parsing, and with
+ * very few code shared between them, this function strips out any options that
+ * we succeed in parsing ourselves. Passing them forward would just give the
+ * underlying fs an option it does not expect, leading it to fail.
+ *
+ * We don't yet have a pointer to the super block as well, since this is
+ * pre-mount. We accumulate in struct vfs_options whatever data we collected,
+ * and act on it later.
+ */
+static int vfs_parse_options(char *options, struct vfs_options *ops)
+{
+ substring_t args[MAX_OPT_ARGS];
+ unsigned int option;
+ char *p;
+ char *opt;
+ char *start = NULL;
+ int ret;
+
+ if (!options)
+ return 0;
+
+ opt = kstrdup(options, GFP_KERNEL);
+ if (!opt)
+ return 1;
+
+ ret = 1;
+
+ start = opt;
+ while ((p = strsep(&opt, ",")) != NULL) {
+ int token;
+ if (!*p)
+ continue;
+
+ /*
+ * Initialize args struct so we know whether arg was
+ * found; some options take optional arguments.
+ */
+ args[0].to = args[0].from = 0;
+ token = match_token(p, tokens, args);
+ switch (token) {
+ case 1:
+ if (!args[0].from)
+ break;
+
+ if (match_int(&args[0], &option))
+ break;
+ else
+ ops->vfs_dcache_size = option;
+
+ ret = 0;
+ if (!opt) /* it is the last option listed */
+ *(options + (p - start)) = '\0';
+ else
+ strcpy(options + (p - start), opt);
+ break;
+ default:
+ ret = 0;
+ break;
+ }
+ }
+
+ kfree(start);
+ return ret;
+}
+
/*
* Flags is a 32-bit value that allows up to 31 non-fs dependent flags to
* be given to the mount() call (ie: read-only, no-dev, no-suid etc).
@@ -2291,6 +2368,7 @@ long do_mount(char *dev_name, char *dir_name, char *type_page,
struct path path;
int retval = 0;
int mnt_flags = 0;
+ struct vfs_options vfs_options;

/* Discard magic */
if ((flags & MS_MGC_MSK) == MS_MGC_VAL)
@@ -2318,6 +2396,12 @@ long do_mount(char *dev_name, char *dir_name, char *type_page,
if (!(flags & MS_NOATIME))
mnt_flags |= MNT_RELATIME;

+
+ vfs_options.vfs_dcache_size = INT_MAX;
+ retval = vfs_parse_options(data_page, &vfs_options);
+ if (retval)
+ goto dput_out;
+
/* Separate the per-mountpoint flags */
if (flags & MS_NOSUID)
mnt_flags |= MNT_NOSUID;
@@ -2350,6 +2434,11 @@ long do_mount(char *dev_name, char *dir_name, char *type_page,
else
retval = do_new_mount(&path, type_page, flags, mnt_flags,
dev_name, data_page);
+
+ if (!retval)
+ vfs_set_dcache_size(path.mnt->mnt_sb,
+ vfs_options.vfs_dcache_size);
+
dput_out:
path_put(&path);
return retval;
--
1.7.6


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