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[src/trunk]: src/sys/fs/tmpfs - Describe some locking.
details: https://anonhg.NetBSD.org/src/rev/6ef9b51ec6cb
branches: trunk
changeset: 765385:6ef9b51ec6cb
user: rmind <rmind%NetBSD.org@localhost>
date: Tue May 24 20:17:49 2011 +0000
description:
- Describe some locking.
- Add VOP argument comments, add some asserts.
- Update/fix/remove outdated/missleading comments.
- Clean up, de-indent, KNF, misc.
No functional changes intended.
diffstat:
sys/fs/tmpfs/tmpfs.h | 331 ++++----------
sys/fs/tmpfs/tmpfs_fifoops.c | 45 +-
sys/fs/tmpfs/tmpfs_fifoops.h | 5 +-
sys/fs/tmpfs/tmpfs_specops.c | 47 +-
sys/fs/tmpfs/tmpfs_specops.h | 6 +-
sys/fs/tmpfs/tmpfs_subr.c | 589 +++++++++-----------------
sys/fs/tmpfs/tmpfs_vfsops.c | 108 +---
sys/fs/tmpfs/tmpfs_vnops.c | 933 ++++++++++++++++++++----------------------
sys/fs/tmpfs/tmpfs_vnops.h | 6 +-
9 files changed, 844 insertions(+), 1226 deletions(-)
diffs (truncated from 3710 to 300 lines):
diff -r e9a3cb322966 -r 6ef9b51ec6cb sys/fs/tmpfs/tmpfs.h
--- a/sys/fs/tmpfs/tmpfs.h Tue May 24 19:12:53 2011 +0000
+++ b/sys/fs/tmpfs/tmpfs.h Tue May 24 20:17:49 2011 +0000
@@ -1,4 +1,4 @@
-/* $NetBSD: tmpfs.h,v 1.40 2011/05/19 03:21:23 rmind Exp $ */
+/* $NetBSD: tmpfs.h,v 1.41 2011/05/24 20:17:49 rmind Exp $ */
/*
* Copyright (c) 2005, 2006, 2007 The NetBSD Foundation, Inc.
@@ -41,93 +41,46 @@
/*
* Internal representation of a tmpfs directory entry.
+ *
+ * All fields are protected by vnode lock.
*/
-struct tmpfs_dirent {
+typedef struct tmpfs_dirent {
TAILQ_ENTRY(tmpfs_dirent) td_entries;
- /* Length of the name stored in this directory entry. This avoids
- * the need to recalculate it every time the name is used. */
- uint16_t td_namelen;
-
- /* The name of the entry, allocated from a string pool. This
- * string is not required to be zero-terminated; therefore, the
- * td_namelen field must always be used when accessing its value. */
- char * td_name;
-
- /* Pointer to the node this entry refers to. */
+ /* Pointer to the inode this entry refers to. */
struct tmpfs_node * td_node;
-};
-/* A directory in tmpfs holds a sorted list of directory entries, which in
- * turn point to other files (which can be directories themselves).
- *
- * In tmpfs, this list is managed by a tail queue, whose head is defined by
- * the struct tmpfs_dir type.
- *
- * It is imporant to notice that directories do not have entries for . and
- * .. as other file systems do. These can be generated when requested
- * based on information available by other means, such as the pointer to
- * the node itself in the former case or the pointer to the parent directory
- * in the latter case. This is done to simplify tmpfs's code and, more
- * importantly, to remove redundancy. */
+ /* Name and its length. */
+ char * td_name;
+ uint16_t td_namelen;
+} tmpfs_dirent_t;
+
TAILQ_HEAD(tmpfs_dir, tmpfs_dirent);
-/* Each entry in a directory has a cookie that identifies it. Cookies
- * supersede offsets within directories because, given how tmpfs stores
- * directories in memory, there is no such thing as an offset. (Emulating
- * a real offset could be very difficult.)
- *
- * The '.', '..' and the end of directory markers have fixed cookies which
- * cannot collide with the cookies generated by other entries. The cookies
- * fot the other entries are generated based on the memory address on which
- * stores their information is stored.
- *
- * Ideally, using the entry's memory pointer as the cookie would be enough
- * to represent it and it wouldn't cause collisions in any system.
- * Unfortunately, this results in "offsets" with very large values which
- * later raise problems in the Linux compatibility layer (and maybe in other
- * places) as described in PR kern/32034. Hence we need to workaround this
- * with a rather ugly hack.
- *
- * Linux 32-bit binaries, unless built with _FILE_OFFSET_BITS=64, have off_t
- * set to 'long', which is a 32-bit *signed* long integer. Regardless of
- * the macro value, GLIBC (2.3 at least) always uses the getdents64
- * system call (when calling readdir) which internally returns off64_t
- * offsets. In order to make 32-bit binaries work, *GLIBC* converts the
- * 64-bit values returned by the kernel to 32-bit ones and aborts with
- * EOVERFLOW if the conversion results in values that won't fit in 32-bit
- * integers (which it assumes is because the directory is extremely large).
- * This wouldn't cause problems if we were dealing with unsigned integers,
- * but as we have signed integers, this check fails due to sign expansion.
- *
- * For example, consider that the kernel returns the 0xc1234567 cookie to
- * userspace in a off64_t integer. Later on, GLIBC casts this value to
- * off_t (remember, signed) with code similar to:
- * system call returns the offset in kernel_value;
- * off_t casted_value = kernel_value;
- * if (sizeof(off_t) != sizeof(off64_t) &&
- * kernel_value != casted_value)
- * error!
- * In this case, casted_value still has 0xc1234567, but when it is compared
- * for equality against kernel_value, it is promoted to a 64-bit integer and
- * becomes 0xffffffffc1234567, which is different than 0x00000000c1234567.
- * Then, GLIBC assumes this is because the directory is very large.
- *
- * Given that all the above happens in user-space, we have no control over
- * it; therefore we must workaround the issue here. We do this by
- * truncating the pointer value to a 32-bit integer and hope that there
- * won't be collisions. In fact, this will not cause any problems in
- * 32-bit platforms but some might arise in 64-bit machines (I'm not sure
- * if they can happen at all in practice).
- *
- * XXX A nicer solution shall be attempted. */
#if defined(_KERNEL)
+
+/* Validate maximum td_namelen length. */
+CTASSERT(MAXNAMLEN < UINT16_MAX);
+
#define TMPFS_DIRCOOKIE_DOT 0
#define TMPFS_DIRCOOKIE_DOTDOT 1
#define TMPFS_DIRCOOKIE_EOF 2
-static __inline
-off_t
-tmpfs_dircookie(struct tmpfs_dirent *de)
+
+/*
+ * Each entry in a directory has a cookie that identifies it. Cookies
+ * supersede offsets within directories, as tmpfs has no offsets as such.
+ *
+ * The '.', '..' and the end of directory markers have fixed cookies,
+ * which cannot collide with the cookies generated by other entries.
+ *
+ * The cookies for the other entries are generated based on the memory
+ * address of their representative meta-data structure.
+ *
+ * XXX: Truncating directory cookies to 31 bits now - workaround for
+ * problem with Linux compat, see PR/32034.
+ */
+static inline off_t
+tmpfs_dircookie(tmpfs_dirent_t *de)
{
off_t cookie;
@@ -138,43 +91,31 @@
return cookie;
}
-#endif /* defined(_KERNEL) */
-
-/* --------------------------------------------------------------------- */
+#endif
/*
- * Internal representation of a tmpfs file system node.
+ * Internal representation of a tmpfs file system node -- inode.
*
* This structure is splitted in two parts: one holds attributes common
* to all file types and the other holds data that is only applicable to
- * a particular type. The code must be careful to only access those
- * attributes that are actually allowed by the node's type.
+ * a particular type.
+ *
+ * All fields are protected by vnode lock. The vnode association itself
+ * is protected by tmpfs_node_t::tn_vlock.
*/
-struct tmpfs_node {
- /* Doubly-linked list entry which links all existing nodes for a
- * single file system. This is provided to ease the removal of
- * all nodes during the unmount operation. */
+typedef struct tmpfs_node {
LIST_ENTRY(tmpfs_node) tn_entries;
- /* The node's type. Any of 'VBLK', 'VCHR', 'VDIR', 'VFIFO',
- * 'VLNK', 'VREG' and 'VSOCK' is allowed. The usage of vnode
- * types instead of a custom enumeration is to make things simpler
- * and faster, as we do not need to convert between two types. */
+ /* The inode type: VBLK, VCHR, VDIR, VFIFO, VLNK, VREG or VSOCK. */
enum vtype tn_type;
- /* Node identifier. */
+ /* Inode identifier. */
ino_t tn_id;
- /* Node's internal status. This is used by several file system
- * operations to do modifications to the node in a delayed
- * fashion. */
+ /* Inode status flags (for operations in delayed manner). */
int tn_status;
-#define TMPFS_NODE_ACCESSED (1 << 1)
-#define TMPFS_NODE_MODIFIED (1 << 2)
-#define TMPFS_NODE_CHANGED (1 << 3)
- /* The node size. It does not necessarily match the real amount
- * of memory consumed by it. */
+ /* The inode size. */
off_t tn_size;
/* Generic node attributes. */
@@ -192,128 +133,105 @@
/* Head of byte-level lock list (used by tmpfs_advlock). */
struct lockf * tn_lockf;
- /* As there is a single vnode for each active file within the
- * system, care has to be taken to avoid allocating more than one
- * vnode per file. In order to do this, a bidirectional association
- * is kept between vnodes and nodes.
+ /*
+ * Each inode has a corresponding vnode. It is a bi-directional
+ * association. Whenever vnode is allocated, its v_data field is
+ * set to the inode it reference, and tmpfs_node_t::tn_vnode is
+ * set to point to the said vnode.
*
- * Whenever a vnode is allocated, its v_data field is updated to
- * point to the node it references. At the same time, the node's
- * tn_vnode field is modified to point to the new vnode representing
- * it. Further attempts to allocate a vnode for this same node will
+ * Further attempts to allocate a vnode for this same node will
* result in returning a new reference to the value stored in
- * tn_vnode.
- *
- * May be NULL when the node is unused (that is, no vnode has been
- * allocated for it or it has been reclaimed). */
+ * tn_vnode. It may be NULL when the node is unused (that is,
+ * no vnode has been allocated or it has been reclaimed).
+ */
kmutex_t tn_vlock;
- struct vnode * tn_vnode;
+ vnode_t * tn_vnode;
union {
- /* Valid when tn_type == VBLK || tn_type == VCHR. */
+ /* Type case: VBLK or VCHR. */
struct {
dev_t tn_rdev;
} tn_dev;
- /* Valid when tn_type == VDIR. */
+ /* Type case: VDIR. */
struct {
- /* Pointer to the parent directory. The root
- * directory has a pointer to itself in this field;
- * this property identifies the root node. */
+ /* Parent directory (root inode points to itself). */
struct tmpfs_node * tn_parent;
- /* Head of a tail-queue that links the contents of
- * the directory together. See above for a
- * description of its contents. */
+ /* List of directory entries. */
struct tmpfs_dir tn_dir;
- /* Number and pointer of the first directory entry
- * returned by the readdir operation if it were
- * called again to continue reading data from the
- * same directory as before. This is used to speed
- * up reads of long directories, assuming that no
- * more than one read is in progress at a given time.
- * Otherwise, these values are discarded and a linear
- * scan is performed from the beginning up to the
- * point where readdir starts returning values. */
+ /*
+ * Number and pointer of the last directory entry
+ * returned by the readdir(3) operation.
+ */
off_t tn_readdir_lastn;
struct tmpfs_dirent * tn_readdir_lastp;
} tn_dir;
- /* Valid when tn_type == VLNK. */
+ /* Type case: VLNK. */
struct tn_lnk {
- /* The link's target, allocated from a string pool. */
+ /* The link's target. */
char * tn_link;
} tn_lnk;
- /* Valid when tn_type == VREG. */
+ /* Type case: VREG. */
struct tn_reg {
- /* The contents of regular files stored in a tmpfs
- * file system are represented by a single anonymous
- * memory object (aobj, for short). The aobj provides
- * direct access to any position within the file,
- * because its contents are always mapped in a
- * contiguous region of virtual memory. It is a task
- * of the memory management subsystem (see uvm(9)) to
- * issue the required page ins or page outs whenever
- * a position within the file is accessed. */
+ /* Underlying UVM object to store contents. */
struct uvm_object * tn_aobj;
size_t tn_aobj_pages;
} tn_reg;
} tn_spec;
-};
-#define TMPFS_NODE_WHITEOUT ((struct tmpfs_node *)-1)
+} tmpfs_node_t;
#if defined(_KERNEL)
+
LIST_HEAD(tmpfs_node_list, tmpfs_node);
-/* --------------------------------------------------------------------- */
+/* Status flags. */
+#define TMPFS_NODE_ACCESSED 0x01
+#define TMPFS_NODE_MODIFIED 0x02
+#define TMPFS_NODE_CHANGED 0x04
+
+#define TMPFS_NODE_STATUSALL \
+ (TMPFS_NODE_ACCESSED | TMPFS_NODE_MODIFIED | TMPFS_NODE_CHANGED)
+
+/* White-out inode indicator. */
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