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Subject[PATCH 05/25] vfs: Implement parameter value retrieval with fsinfo() [ver #14]
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Date
Implement parameter value retrieval with fsinfo() - akin to parsing
/proc/mounts.

This allows all the parameters to be retrieved in one go with:

struct fsinfo_params params = {
.request = FSINFO_ATTR_PARAMETER,
};

Each parameter comes as a pair of blobs with a length tacked on the front
rather than using separators, since any printable character that could be
used as a separator can be found in some value somewhere (including comma).
In fact, cifs allows the separator to be set using the "sep=" option in
parameter parsing.

The length on the front of each blob is 1-3 bytes long. Each byte has a
flag in bit 7 that's set if there are more bytes and clear on the last
byte; bits 0-6 should be shifted and OR'd into the length count. The bytes
are most-significant first.

For example, 0x83 0xf5 0x06 is the length (0x03<<14 | 0x75<<7 | 0x06).

As mentioned, each parameter comes as a pair of blobs in key, value order.
The value has length zero if not present. So, for example:

\x08compress\x04zlib

from btrfs would be equivalent to "compress=zlib" and:

\x02ro\x00\x06noexec\x00

would be equivalent to "ro,noexec".

The test-fsinfo sample program is modified to dump the parameters.

Signed-off-by: David Howells <dhowells@redhat.com>
---

fs/fsinfo.c | 122 +++++++++++++++++++++++++++++++++++++++++++
include/linux/fsinfo.h | 4 +
include/uapi/linux/fsinfo.h | 1
samples/vfs/test-fsinfo.c | 38 +++++++++++++
4 files changed, 165 insertions(+)

diff --git a/fs/fsinfo.c b/fs/fsinfo.c
index 9e2a25510b88..3b35cedab0df 100644
--- a/fs/fsinfo.c
+++ b/fs/fsinfo.c
@@ -296,6 +296,32 @@ static int fsinfo_generic_param_enum(struct file_system_type *f,
return sizeof(*p);
}

+void fsinfo_note_sb_params(struct fsinfo_kparams *params, unsigned int s_flags)
+{
+ if (s_flags & SB_DIRSYNC)
+ fsinfo_note_param(params, "dirsync", NULL);
+ if (s_flags & SB_LAZYTIME)
+ fsinfo_note_param(params, "lazytime", NULL);
+ if (s_flags & SB_MANDLOCK)
+ fsinfo_note_param(params, "mand", NULL);
+ if (s_flags & SB_POSIXACL)
+ fsinfo_note_param(params, "posixacl", NULL);
+ if (s_flags & SB_RDONLY)
+ fsinfo_note_param(params, "ro", NULL);
+ else
+ fsinfo_note_param(params, "rw", NULL);
+ if (s_flags & SB_SYNCHRONOUS)
+ fsinfo_note_param(params, "sync", NULL);
+}
+EXPORT_SYMBOL(fsinfo_note_sb_params);
+
+static int fsinfo_generic_parameters(struct path *path,
+ struct fsinfo_kparams *params)
+{
+ fsinfo_note_sb_params(params, READ_ONCE(path->dentry->d_sb->s_flags));
+ return params->usage;
+}
+
/*
* Implement some queries generically from stuff in the superblock.
*/
@@ -304,6 +330,7 @@ int generic_fsinfo(struct path *path, struct fsinfo_kparams *params)
struct file_system_type *fs = path->dentry->d_sb->s_type;

#define _gen(X, Y) FSINFO_ATTR_##X: return fsinfo_generic_##Y(path, params->buffer)
+#define _genp(X, Y) FSINFO_ATTR_##X: return fsinfo_generic_##Y(path, params)
#define _genf(X, Y) FSINFO_ATTR_##X: return fsinfo_generic_##Y(fs, params)

switch (params->request) {
@@ -319,6 +346,7 @@ int generic_fsinfo(struct path *path, struct fsinfo_kparams *params)
case _genf(PARAM_DESCRIPTION, param_description);
case _genf(PARAM_SPECIFICATION, param_specification);
case _genf(PARAM_ENUM, param_enum);
+ case _genp(PARAMETERS, parameters);
default:
return -EOPNOTSUPP;
}
@@ -358,8 +386,16 @@ static int vfs_fsinfo(struct path *path, struct fsinfo_kparams *params)
return fsinfo(path, params);

while (!signal_pending(current)) {
+ if (params->request == FSINFO_ATTR_PARAMETERS) {
+ if (down_read_killable(&dentry->d_sb->s_umount) < 0)
+ return -ERESTARTSYS;
+ }
+
params->usage = 0;
ret = fsinfo(path, params);
+ if (params->request == FSINFO_ATTR_PARAMETERS)
+ up_read(&dentry->d_sb->s_umount);
+
if (ret <= (int)params->buf_size)
return ret; /* Error or it fitted */
kvfree(params->buffer);
@@ -529,6 +565,7 @@ static const struct fsinfo_attr_info fsinfo_buffer_info[FSINFO_ATTR__NR] = {
FSINFO_STRUCT (PARAM_DESCRIPTION, param_description),
FSINFO_STRUCT_N (PARAM_SPECIFICATION, param_specification),
FSINFO_STRUCT_N (PARAM_ENUM, param_enum),
+ FSINFO_OPAQUE (PARAMETERS, -),
};

/**
@@ -676,3 +713,88 @@ SYSCALL_DEFINE5(fsinfo,
error:
return ret;
}
+
+/*
+ * Store a parameter into the user's parameter buffer. The key is prefixed by
+ * a single byte length (1-127) and the value by one (0-0x7f) or two bytes
+ * (0x80-0x3fff) or three bytes (0x4000-0x1fffff).
+ *
+ * Note that we must always make the size determination, even if the buffer is
+ * already full, so that we can tell the caller how much buffer we actually
+ * need.
+ */
+static void __fsinfo_note_param(struct fsinfo_kparams *params, const char *key,
+ const char *val, unsigned int vlen)
+{
+ char *p;
+ unsigned int usage;
+ int klen, total, vmeta;
+ u8 x;
+
+ klen = strlen(key);
+ BUG_ON(klen < 1 || klen > 127);
+ BUG_ON(vlen > (1 << 21) - 1);
+ BUG_ON(vlen > 0 && !val);
+
+ vmeta = (vlen <= 127) ? 1 : (vlen <= 127 * 127) ? 2 : 3;
+
+ total = 1 + klen + vmeta + vlen;
+
+ usage = params->usage;
+ params->usage = usage + total;
+ if (!params->buffer || params->usage > params->buf_size)
+ return;
+
+ p = params->buffer + usage;
+ *p++ = klen;
+ p = memcpy(p, key, klen);
+ p += klen;
+
+ /* The more significant groups of 7 bits in the size are included in
+ * most->least order with 0x80 OR'd in. The least significant 7 bits
+ * are last with the top bit clear.
+ */
+ x = vlen >> 14;
+ if (x & 0x7f)
+ *p++ = 0x80 | x;
+
+ x = vlen >> 7;
+ if (x & 0x7f)
+ *p++ = 0x80 | x;
+
+ *p++ = vlen & 0x7f;
+ memcpy(p, val, vlen);
+}
+
+/**
+ * fsinfo_note_param - Store a parameter for FSINFO_ATTR_PARAMETERS
+ * @params: The parameter buffer
+ * @key: The parameter's key
+ * @val: The parameter's value (or NULL)
+ */
+void fsinfo_note_param(struct fsinfo_kparams *params, const char *key,
+ const char *val)
+{
+ __fsinfo_note_param(params, key, val, val ? strlen(val) : 0);
+}
+EXPORT_SYMBOL(fsinfo_note_param);
+
+/**
+ * fsinfo_note_paramf - Store a formatted parameter for FSINFO_ATTR_PARAMETERS
+ * @params: The parameter buffer
+ * @key: The parameter's key
+ * @val_fmt: Format string for the parameter's value
+ */
+void fsinfo_note_paramf(struct fsinfo_kparams *params, const char *key,
+ const char *val_fmt, ...)
+{
+ va_list va;
+ int n;
+
+ va_start(va, val_fmt);
+ n = vsnprintf(params->scratch_buffer, 4096, val_fmt, va);
+ va_end(va);
+
+ __fsinfo_note_param(params, key, params->scratch_buffer, n);
+}
+EXPORT_SYMBOL(fsinfo_note_paramf);
diff --git a/include/linux/fsinfo.h b/include/linux/fsinfo.h
index e17e4f0bae18..731931afbf1c 100644
--- a/include/linux/fsinfo.h
+++ b/include/linux/fsinfo.h
@@ -29,6 +29,10 @@ struct fsinfo_kparams {
};

extern int generic_fsinfo(struct path *, struct fsinfo_kparams *);
+extern void fsinfo_note_sb_params(struct fsinfo_kparams *, unsigned int);
+extern void fsinfo_note_param(struct fsinfo_kparams *, const char *, const char *);
+extern void fsinfo_note_paramf(struct fsinfo_kparams *, const char *, const char *, ...)
+ __printf(3, 4);

static inline void fsinfo_set_cap(struct fsinfo_capabilities *c,
enum fsinfo_capability cap)
diff --git a/include/uapi/linux/fsinfo.h b/include/uapi/linux/fsinfo.h
index 9d929d2f7eee..475cd1c97b12 100644
--- a/include/uapi/linux/fsinfo.h
+++ b/include/uapi/linux/fsinfo.h
@@ -30,6 +30,7 @@ enum fsinfo_attribute {
FSINFO_ATTR_PARAM_DESCRIPTION = 12, /* General fs parameter description */
FSINFO_ATTR_PARAM_SPECIFICATION = 13, /* Nth parameter specification */
FSINFO_ATTR_PARAM_ENUM = 14, /* Nth enum-to-val */
+ FSINFO_ATTR_PARAMETERS = 15, /* Mount parameters (large string) */
FSINFO_ATTR__NR
};

diff --git a/samples/vfs/test-fsinfo.c b/samples/vfs/test-fsinfo.c
index 3c6ea3a5c157..8cf5b02e333a 100644
--- a/samples/vfs/test-fsinfo.c
+++ b/samples/vfs/test-fsinfo.c
@@ -81,6 +81,7 @@ static const struct fsinfo_attr_info fsinfo_buffer_info[FSINFO_ATTR__NR] = {
FSINFO_STRUCT (PARAM_DESCRIPTION, param_description),
FSINFO_STRUCT_N (PARAM_SPECIFICATION, param_specification),
FSINFO_STRUCT_N (PARAM_ENUM, param_enum),
+ FSINFO_OVERLARGE (PARAMETERS, -),
};

#define FSINFO_NAME(X,Y) [FSINFO_ATTR_##X] = #Y
@@ -100,6 +101,7 @@ static const char *fsinfo_attr_names[FSINFO_ATTR__NR] = {
FSINFO_NAME (PARAM_DESCRIPTION, param_description),
FSINFO_NAME (PARAM_SPECIFICATION, param_specification),
FSINFO_NAME (PARAM_ENUM, param_enum),
+ FSINFO_NAME (PARAMETERS, parameters),
};

union reply {
@@ -352,6 +354,34 @@ static void dump_fsinfo(enum fsinfo_attribute attr,
dumper(r, size);
}

+static void dump_params(struct fsinfo_attr_info about, union reply *r, int size)
+{
+ int len;
+ char *p = r->buffer, *e = p + size;
+ bool is_key = true;
+
+ while (p < e) {
+ len = 0;
+ while (p[0] & 0x80) {
+ len <<= 7;
+ len |= *p++ & 0x7f;
+ }
+
+ len <<= 7;
+ len |= *p++;
+ if (len > e - p)
+ break;
+ if (is_key || len)
+ printf("%s%*.*s", is_key ? "[PARM] " : "= ", len, len, p);
+ if (is_key)
+ putchar(' ');
+ else
+ putchar('\n');
+ p += len;
+ is_key = !is_key;
+ }
+}
+
/*
* Try one subinstance of an attribute.
*/
@@ -427,6 +457,12 @@ static int try_one(const char *file, struct fsinfo_params *params, bool raw)
return 0;
}

+ switch (params->request) {
+ case FSINFO_ATTR_PARAMETERS:
+ if (ret == 0)
+ return 0;
+ }
+
switch (about.flags & (__FSINFO_N | __FSINFO_NM)) {
case 0:
printf("\e[33m%s\e[m: ",
@@ -469,6 +505,8 @@ static int try_one(const char *file, struct fsinfo_params *params, bool raw)
return 0;

case __FSINFO_OVER:
+ if (params->request == FSINFO_ATTR_PARAMETERS)
+ dump_params(about, r, ret);
return 0;

case __FSINFO_STRUCT_ARRAY:
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