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authorDavid Howells <dhowells@redhat.com>2018-11-01 23:34:29 +0000
committerAl Viro <viro@zeniv.linux.org.uk>2019-03-20 18:49:06 -0400
commit007ec26cdc9fefacbed85b592afc69413194499c (patch)
tree757bc7472e25a91db0109784d4b2da59ed23554b /fs/fs_context.c
parent24dcb3d90a1f67fe08c68a004af37df059d74005 (diff)
vfs: Implement logging through fs_context
Implement the ability for filesystems to log error, warning and informational messages through the fs_context. These can be extracted by userspace by reading from an fd created by fsopen(). Error messages are prefixed with "e ", warnings with "w " and informational messages with "i ". Inside the kernel, formatted messages are malloc'd but unformatted messages are not copied if they're either in the core .rodata section or in the .rodata section of the filesystem module pinned by fs_context::fs_type. The messages are only good till the fs_type is released. Note that the logging object is shared between duplicated fs_context structures. This is so that such as NFS which do a mount within a mount can get at least some of the errors from the inner mount. Five logging functions are provided for this: (1) void logfc(struct fs_context *fc, const char *fmt, ...); This logs a message into the context. If the buffer is full, the earliest message is discarded. (2) void errorf(fc, fmt, ...); This wraps logfc() to log an error. (3) void invalf(fc, fmt, ...); This wraps errorf() and returns -EINVAL for convenience. (4) void warnf(fc, fmt, ...); This wraps logfc() to log a warning. (5) void infof(fc, fmt, ...); This wraps logfc() to log an informational message. Signed-off-by: David Howells <dhowells@redhat.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Diffstat (limited to 'fs/fs_context.c')
-rw-r--r--fs/fs_context.c105
1 files changed, 91 insertions, 14 deletions
diff --git a/fs/fs_context.c b/fs/fs_context.c
index eb806fae3117..dcf3786f90f9 100644
--- a/fs/fs_context.c
+++ b/fs/fs_context.c
@@ -11,6 +11,7 @@
*/
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+#include <linux/module.h>
#include <linux/fs_context.h>
#include <linux/fs_parser.h>
#include <linux/fs.h>
@@ -23,6 +24,7 @@
#include <linux/pid_namespace.h>
#include <linux/user_namespace.h>
#include <net/net_namespace.h>
+#include <asm/sections.h>
#include "mount.h"
#include "internal.h"
@@ -365,6 +367,8 @@ struct fs_context *vfs_dup_fs_context(struct fs_context *src_fc)
get_net(fc->net_ns);
get_user_ns(fc->user_ns);
get_cred(fc->cred);
+ if (fc->log)
+ refcount_inc(&fc->log->usage);
/* Can't call put until we've called ->dup */
ret = fc->ops->dup(fc, src_fc);
@@ -382,7 +386,6 @@ err_fc:
}
EXPORT_SYMBOL(vfs_dup_fs_context);
-#ifdef CONFIG_PRINTK
/**
* logfc - Log a message to a filesystem context
* @fc: The filesystem context to log to.
@@ -390,27 +393,100 @@ EXPORT_SYMBOL(vfs_dup_fs_context);
*/
void logfc(struct fs_context *fc, const char *fmt, ...)
{
+ static const char store_failure[] = "OOM: Can't store error string";
+ struct fc_log *log = fc ? fc->log : NULL;
+ const char *p;
va_list va;
+ char *q;
+ u8 freeable;
va_start(va, fmt);
-
- switch (fmt[0]) {
- case 'w':
- vprintk_emit(0, LOGLEVEL_WARNING, NULL, 0, fmt, va);
- break;
- case 'e':
- vprintk_emit(0, LOGLEVEL_ERR, NULL, 0, fmt, va);
- break;
- default:
- vprintk_emit(0, LOGLEVEL_NOTICE, NULL, 0, fmt, va);
- break;
+ if (!strchr(fmt, '%')) {
+ p = fmt;
+ goto unformatted_string;
}
+ if (strcmp(fmt, "%s") == 0) {
+ p = va_arg(va, const char *);
+ goto unformatted_string;
+ }
+
+ q = kvasprintf(GFP_KERNEL, fmt, va);
+copied_string:
+ if (!q)
+ goto store_failure;
+ freeable = 1;
+ goto store_string;
+
+unformatted_string:
+ if ((unsigned long)p >= (unsigned long)__start_rodata &&
+ (unsigned long)p < (unsigned long)__end_rodata)
+ goto const_string;
+ if (log && within_module_core((unsigned long)p, log->owner))
+ goto const_string;
+ q = kstrdup(p, GFP_KERNEL);
+ goto copied_string;
+
+store_failure:
+ p = store_failure;
+const_string:
+ q = (char *)p;
+ freeable = 0;
+store_string:
+ if (!log) {
+ switch (fmt[0]) {
+ case 'w':
+ printk(KERN_WARNING "%s\n", q + 2);
+ break;
+ case 'e':
+ printk(KERN_ERR "%s\n", q + 2);
+ break;
+ default:
+ printk(KERN_NOTICE "%s\n", q + 2);
+ break;
+ }
+ if (freeable)
+ kfree(q);
+ } else {
+ unsigned int logsize = ARRAY_SIZE(log->buffer);
+ u8 index;
+
+ index = log->head & (logsize - 1);
+ BUILD_BUG_ON(sizeof(log->head) != sizeof(u8) ||
+ sizeof(log->tail) != sizeof(u8));
+ if ((u8)(log->head - log->tail) == logsize) {
+ /* The buffer is full, discard the oldest message */
+ if (log->need_free & (1 << index))
+ kfree(log->buffer[index]);
+ log->tail++;
+ }
- pr_cont("\n");
+ log->buffer[index] = q;
+ log->need_free &= ~(1 << index);
+ log->need_free |= freeable << index;
+ log->head++;
+ }
va_end(va);
}
EXPORT_SYMBOL(logfc);
-#endif
+
+/*
+ * Free a logging structure.
+ */
+static void put_fc_log(struct fs_context *fc)
+{
+ struct fc_log *log = fc->log;
+ int i;
+
+ if (log) {
+ if (refcount_dec_and_test(&log->usage)) {
+ fc->log = NULL;
+ for (i = 0; i <= 7; i++)
+ if (log->need_free & (1 << i))
+ kfree(log->buffer[i]);
+ kfree(log);
+ }
+ }
+}
/**
* put_fs_context - Dispose of a superblock configuration context.
@@ -435,6 +511,7 @@ void put_fs_context(struct fs_context *fc)
put_user_ns(fc->user_ns);
put_cred(fc->cred);
kfree(fc->subtype);
+ put_fc_log(fc);
put_filesystem(fc->fs_type);
kfree(fc->source);
kfree(fc);