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Message-ID: <20251118022655.126994-2-rajasimandalos@gmail.com>
Date: Tue, 18 Nov 2025 02:26:55 +0000
From: Rajasi Mandal <rajasimandalos@...il.com>
To: sfrench@...ba.org,
linux-cifs@...r.kernel.org
Cc: pc@...guebit.org,
ronniesahlberg@...il.com,
sprasad@...rosoft.com,
tom@...pey.com,
bharathsm@...rosoft.com,
samba-technical@...ts.samba.org,
linux-kernel@...r.kernel.org,
Rajasi Mandal <rajasimandal@...rosoft.com>
Subject: [PATCH] cifs: client: enforce consistent handling of multichannel and max_channels
From: Rajasi Mandal <rajasimandal@...rosoft.com>
Previously, the behavior of the multichannel and max_channels mount
options was inconsistent and order-dependent. For example, specifying
"multichannel,max_channels=1" would result in 2 channels, while
"max_channels=1,multichannel" would result in 1 channel. Additionally,
conflicting combinations such as "nomultichannel,max_channels=3" or
"multichannel,max_channels=1" did not produce errors and could lead to
unexpected channel counts.
This commit introduces two new fields in smb3_fs_context to explicitly
track whether multichannel and max_channels were specified during
mount. The option parsing and validation logic is updated to ensure:
- The outcome is no longer dependent on the order of options.
- Conflicting combinations (e.g., "nomultichannel,max_channels=3" or
"multichannel,max_channels=1") are detected and result in an error.
- The number of channels created is consistent with the specified
options.
This improves the reliability and predictability of mount option
handling for SMB3 multichannel support.
Reviewed-by: Shyam Prasad N <sprasad@...rosoft.com>
Signed-off-by: Rajasi Mandal <rajasimandal@...rosoft.com>
---
fs/smb/client/cifsfs.c | 1 -
fs/smb/client/fs_context.c | 65 ++++++++++++++++++++++++++++----------
fs/smb/client/fs_context.h | 2 ++
3 files changed, 50 insertions(+), 18 deletions(-)
diff --git a/fs/smb/client/cifsfs.c b/fs/smb/client/cifsfs.c
index 185ac41bd7e9..4d53ec53d8db 100644
--- a/fs/smb/client/cifsfs.c
+++ b/fs/smb/client/cifsfs.c
@@ -1016,7 +1016,6 @@ cifs_smb3_do_mount(struct file_system_type *fs_type,
} else {
cifs_info("Attempting to mount %s\n", old_ctx->source);
}
-
cifs_sb = kzalloc(sizeof(*cifs_sb), GFP_KERNEL);
if (!cifs_sb)
return ERR_PTR(-ENOMEM);
diff --git a/fs/smb/client/fs_context.c b/fs/smb/client/fs_context.c
index 46d1eaae62da..1794a31541fe 100644
--- a/fs/smb/client/fs_context.c
+++ b/fs/smb/client/fs_context.c
@@ -711,6 +711,47 @@ smb3_parse_devname(const char *devname, struct smb3_fs_context *ctx)
return 0;
}
+static int smb3_handle_conflicting_options(struct fs_context *fc)
+{
+ struct smb3_fs_context *ctx = smb3_fc2context(fc);
+
+ if (ctx->multichannel_specified) {
+ if (ctx->multichannel) {
+ if (!ctx->max_channels_specified) {
+ ctx->max_channels = 2;
+ } else if (ctx->max_channels == 1) {
+ cifs_errorf(fc,
+ "max_channels must be greater than 1 when multichannel is enabled\n");
+ return -EINVAL;
+ }
+ } else {
+ if (!ctx->max_channels_specified) {
+ ctx->max_channels = 1;
+ } else if (ctx->max_channels > 1) {
+ cifs_errorf(fc,
+ "max_channels must be equal to 1 when multichannel is disabled\n");
+ return -EINVAL;
+ }
+ }
+ } else {
+ if (ctx->max_channels_specified) {
+ if (ctx->max_channels > 1)
+ ctx->multichannel = true;
+ else
+ ctx->multichannel = false;
+ } else {
+ ctx->multichannel = false;
+ ctx->max_channels = 1;
+ }
+ }
+
+ //resetting default values as remount doesn't initialize fs_context again
+ ctx->multichannel_specified = false;
+ ctx->max_channels_specified = false;
+
+ return 0;
+}
+
static void smb3_fs_context_free(struct fs_context *fc);
static int smb3_fs_context_parse_param(struct fs_context *fc,
struct fs_parameter *param);
@@ -785,6 +826,7 @@ static int smb3_fs_context_parse_monolithic(struct fs_context *fc,
if (ret < 0)
break;
}
+ ret = smb3_handle_conflicting_options(fc);
return ret;
}
@@ -1296,15 +1338,11 @@ static int smb3_fs_context_parse_param(struct fs_context *fc,
ctx->nodelete = 1;
break;
case Opt_multichannel:
- if (result.negated) {
+ ctx->multichannel_specified = true;
+ if (result.negated)
ctx->multichannel = false;
- ctx->max_channels = 1;
- } else {
+ else
ctx->multichannel = true;
- /* if number of channels not specified, default to 2 */
- if (ctx->max_channels < 2)
- ctx->max_channels = 2;
- }
break;
case Opt_uid:
ctx->linux_uid = result.uid;
@@ -1440,15 +1478,13 @@ static int smb3_fs_context_parse_param(struct fs_context *fc,
ctx->max_credits = result.uint_32;
break;
case Opt_max_channels:
+ ctx->max_channels_specified = true;
if (result.uint_32 < 1 || result.uint_32 > CIFS_MAX_CHANNELS) {
cifs_errorf(fc, "%s: Invalid max_channels value, needs to be 1-%d\n",
__func__, CIFS_MAX_CHANNELS);
goto cifs_parse_mount_err;
}
ctx->max_channels = result.uint_32;
- /* If more than one channel requested ... they want multichan */
- if (result.uint_32 > 1)
- ctx->multichannel = true;
break;
case Opt_max_cached_dirs:
if (result.uint_32 < 1) {
@@ -1866,13 +1902,6 @@ static int smb3_fs_context_parse_param(struct fs_context *fc,
goto cifs_parse_mount_err;
}
- /*
- * Multichannel is not meaningful if max_channels is 1.
- * Force multichannel to false to ensure consistent configuration.
- */
- if (ctx->multichannel && ctx->max_channels == 1)
- ctx->multichannel = false;
-
return 0;
cifs_parse_mount_err:
@@ -1955,6 +1984,8 @@ int smb3_init_fs_context(struct fs_context *fc)
/* default to no multichannel (single server connection) */
ctx->multichannel = false;
+ ctx->multichannel_specified = false;
+ ctx->max_channels_specified = false;
ctx->max_channels = 1;
ctx->backupuid_specified = false; /* no backup intent for a user */
diff --git a/fs/smb/client/fs_context.h b/fs/smb/client/fs_context.h
index b0fec6b9a23b..7af7cbbe4208 100644
--- a/fs/smb/client/fs_context.h
+++ b/fs/smb/client/fs_context.h
@@ -294,6 +294,8 @@ struct smb3_fs_context {
bool domainauto:1;
bool rdma:1;
bool multichannel:1;
+ bool multichannel_specified:1; /* true if user specified multichannel or nomultichannel */
+ bool max_channels_specified:1; /* true if user specified max_channels */
bool use_client_guid:1;
/* reuse existing guid for multichannel */
u8 client_guid[SMB2_CLIENT_GUID_SIZE];
--
2.43.0
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