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9p: Add mount option for negative dentry cache retention

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Introduce a new mount option, negtimeout, for v9fs that allows users
to specify how long negative dentries are retained in the cache. The
retention time can be set in milliseconds (e.g. negtimeout=10000 for
a 10secs retention time) or a negative value (e.g. negtimeout=-1) to
keep negative entries until the buffer cache management removes them.

For consistency reasons, this option should only be used in exclusive
or read-only mount scenarios, aligning with the cache=loose usage.

Signed-off-by: Remi Pommarel <repk@triplefau.lt>
Message-ID: <b2d66500aa5a2f6540347c4aa46a4be10dd01bc6.1779355927.git.repk@triplefau.lt>
Signed-off-by: Dominique Martinet <asmadeus@codewreck.org>
This commit is contained in:
Remi Pommarel
2026-05-21 11:40:30 +02:00
committed by Dominique Martinet
parent f00e6c1d28
commit 5670a84b5c
3 changed files with 33 additions and 11 deletions
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5
Documentation/filesystems/9p.rst
View File

@@ -235,6 +235,11 @@ Options
cachetag cache tag to use the specified persistent cache.
cache tags for existing cache sessions can be listed at
/sys/fs/9p/caches. (applies only to cache=fscache)
negtimeout the duration (in milliseconds) that negative dentries (paths
that do not actually exist) are retained in the cache. If
set to a negative value, those entries are kept indefinitely
until evicted by the buffer cache management system
============= ===============================================================
Behavior

16
fs/9p/v9fs.c
View File

@@ -39,7 +39,7 @@ enum {
* source if we rejected it as EINVAL */
Opt_source,
/* Options that take integer arguments */
Opt_debug, Opt_dfltuid, Opt_dfltgid, Opt_afid,
Opt_debug, Opt_dfltuid, Opt_dfltgid, Opt_afid, Opt_negtimeout,
/* String options */
Opt_uname, Opt_remotename, Opt_cache, Opt_cachetag,
/* Options that take no arguments */
@@ -93,6 +93,7 @@ const struct fs_parameter_spec v9fs_param_spec[] = {
fsparam_string ("access", Opt_access),
fsparam_flag ("posixacl", Opt_posixacl),
fsparam_u32 ("locktimeout", Opt_locktimeout),
fsparam_s32 ("negtimeout", Opt_negtimeout),
/* client options */
fsparam_u32 ("msize", Opt_msize),
@@ -159,6 +160,9 @@ int v9fs_show_options(struct seq_file *m, struct dentry *root)
from_kgid_munged(&init_user_ns, v9ses->dfltgid));
if (v9ses->afid != ~0)
seq_printf(m, ",afid=%u", v9ses->afid);
if (v9ses->flags & V9FS_NDENTRY_TIMEOUT_SET)
seq_printf(m, ",negtimeout=%d",
(int)v9ses->ndentry_timeout_ms);
if (strcmp(v9ses->uname, V9FS_DEFUSER) != 0)
seq_printf(m, ",uname=%s", v9ses->uname);
if (strcmp(v9ses->aname, V9FS_DEFANAME) != 0)
@@ -337,6 +341,16 @@ int v9fs_parse_param(struct fs_context *fc, struct fs_parameter *param)
session_opts->session_lock_timeout = (long)result.uint_32 * HZ;
break;
case Opt_negtimeout:
session_opts->flags |= V9FS_NDENTRY_TIMEOUT_SET;
if (result.int_32 < 0) {
session_opts->ndentry_timeout_ms =
NDENTRY_TIMEOUT_NEVER;
} else {
session_opts->ndentry_timeout_ms = result.int_32;
}
break;
/* Options for client */
case Opt_msize:
if (result.uint_32 < 4096) {

23
fs/9p/v9fs.h
View File

@@ -24,6 +24,8 @@
* @V9FS_ACCESS_ANY: use a single attach for all users
* @V9FS_ACCESS_MASK: bit mask of different ACCESS options
* @V9FS_POSIX_ACL: POSIX ACLs are enforced
* @V9FS_NDENTRY_TIMEOUT_SET: Has negative dentry timeout retention time been
* overridden by negtimeout mount option
*
* Session flags reflect options selected by users at mount time
*/
@@ -34,16 +36,17 @@
#define V9FS_ACL_MASK V9FS_POSIX_ACL
enum p9_session_flags {
V9FS_PROTO_2000U = 0x01,
V9FS_PROTO_2000L = 0x02,
V9FS_ACCESS_SINGLE = 0x04,
V9FS_ACCESS_USER = 0x08,
V9FS_ACCESS_CLIENT = 0x10,
V9FS_POSIX_ACL = 0x20,
V9FS_NO_XATTR = 0x40,
V9FS_IGNORE_QV = 0x80, /* ignore qid.version for cache hints */
V9FS_DIRECT_IO = 0x100,
V9FS_SYNC = 0x200
V9FS_PROTO_2000U = 0x01,
V9FS_PROTO_2000L = 0x02,
V9FS_ACCESS_SINGLE = 0x04,
V9FS_ACCESS_USER = 0x08,
V9FS_ACCESS_CLIENT = 0x10,
V9FS_POSIX_ACL = 0x20,
V9FS_NO_XATTR = 0x40,
V9FS_IGNORE_QV = 0x80, /* ignore qid.version for cache hints */
V9FS_DIRECT_IO = 0x100,
V9FS_SYNC = 0x200,
V9FS_NDENTRY_TIMEOUT_SET = 0x400,
};
/**