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scsi: core: Introduce a new list for SCSI proc directory entries
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Instead of using scsi_host_template members to track the SCSI proc
directory entries, track these entries in a list. This changes the time
needed for looking up the proc dir pointer from O(1) into O(n). This is
considered acceptable since the number of SCSI host adapter types per host
is usually small (less than ten).

This change has been tested by attaching two USB storage devices to a qemu
host:

$ grep -aH . /proc/scsi/usb-storage/*
/proc/scsi/usb-storage/7:   Host scsi7: usb-storage
/proc/scsi/usb-storage/7:       Vendor: QEMU
/proc/scsi/usb-storage/7:      Product: QEMU USB HARDDRIVE
/proc/scsi/usb-storage/7:Serial Number: 1-0000:00:02.1:00.0-6
/proc/scsi/usb-storage/7:     Protocol: Transparent SCSI
/proc/scsi/usb-storage/7:    Transport: Bulk
/proc/scsi/usb-storage/7:       Quirks: SANE_SENSE
/proc/scsi/usb-storage/8:   Host scsi8: usb-storage
/proc/scsi/usb-storage/8:       Vendor: QEMU
/proc/scsi/usb-storage/8:      Product: QEMU USB HARDDRIVE
/proc/scsi/usb-storage/8:Serial Number: 1-0000:00:02.1:00.0-7
/proc/scsi/usb-storage/8:     Protocol: Transparent SCSI
/proc/scsi/usb-storage/8:    Transport: Bulk
/proc/scsi/usb-storage/8:       Quirks: SANE_SENSE

This commit prepares for constifying most SCSI host templates.

Reviewed-by: John Garry <[email protected]>
Cc: Christoph Hellwig <[email protected]>
Cc: Ming Lei <[email protected]>
Cc: Hannes Reinecke <[email protected]>
Cc: Mike Christie <[email protected]>
Cc: Krzysztof Kozlowski <[email protected]>
Signed-off-by: Bart Van Assche <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Martin K. Petersen <[email protected]>
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@bvanassche @martinkpetersen
bvanassche authored and martinkpetersen committed Oct 18, 2022
1 parent ecca3f9 commit 036abd6
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Showing 3 changed files with 102 additions and 35 deletions.
4 changes: 2 additions & 2 deletions drivers/scsi/scsi_priv.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -111,8 +111,8 @@ extern void scsi_evt_thread(struct work_struct *work);

/* scsi_proc.c */
#ifdef CONFIG_SCSI_PROC_FS
extern int scsi_proc_hostdir_add(struct scsi_host_template *);
extern void scsi_proc_hostdir_rm(struct scsi_host_template *);
extern int scsi_proc_hostdir_add(const struct scsi_host_template *);
extern void scsi_proc_hostdir_rm(const struct scsi_host_template *);
extern void scsi_proc_host_add(struct Scsi_Host *);
extern void scsi_proc_host_rm(struct Scsi_Host *);
extern int scsi_init_procfs(void);
Expand Down
121 changes: 100 additions & 21 deletions drivers/scsi/scsi_proc.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -43,8 +43,23 @@

static struct proc_dir_entry *proc_scsi;

/* Protect sht->present and sht->proc_dir */
/* Protects scsi_proc_list */
static DEFINE_MUTEX(global_host_template_mutex);
static LIST_HEAD(scsi_proc_list);

/**
* struct scsi_proc_entry - (host template, SCSI proc dir) association
* @entry: entry in scsi_proc_list.
* @sht: SCSI host template associated with the procfs directory.
* @proc_dir: procfs directory associated with the SCSI host template.
* @present: Number of SCSI hosts instantiated for @sht.
*/
struct scsi_proc_entry {
struct list_head entry;
const struct scsi_host_template *sht;
struct proc_dir_entry *proc_dir;
unsigned int present;
};

static ssize_t proc_scsi_host_write(struct file *file, const char __user *buf,
size_t count, loff_t *ppos)
Expand Down Expand Up @@ -83,14 +98,42 @@ static int proc_scsi_host_open(struct inode *inode, struct file *file)
4 * PAGE_SIZE);
}

static struct scsi_proc_entry *
__scsi_lookup_proc_entry(const struct scsi_host_template *sht)
{
struct scsi_proc_entry *e;

lockdep_assert_held(&global_host_template_mutex);

list_for_each_entry(e, &scsi_proc_list, entry)
if (e->sht == sht)
return e;

return NULL;
}

static struct scsi_proc_entry *
scsi_lookup_proc_entry(const struct scsi_host_template *sht)
{
struct scsi_proc_entry *e;

mutex_lock(&global_host_template_mutex);
e = __scsi_lookup_proc_entry(sht);
mutex_unlock(&global_host_template_mutex);

return e;
}

/**
* scsi_template_proc_dir() - returns the procfs dir for a SCSI host template
* @sht: SCSI host template pointer.
*/
struct proc_dir_entry *
scsi_template_proc_dir(const struct scsi_host_template *sht)
{
return sht->proc_dir;
struct scsi_proc_entry *e = scsi_lookup_proc_entry(sht);

return e ? e->proc_dir : NULL;
}
EXPORT_SYMBOL_GPL(scsi_template_proc_dir);

Expand All @@ -108,40 +151,61 @@ static const struct proc_ops proc_scsi_ops = {
*
* Sets sht->proc_dir to the new directory.
*/
int scsi_proc_hostdir_add(struct scsi_host_template *sht)
int scsi_proc_hostdir_add(const struct scsi_host_template *sht)
{
int ret = 0;
struct scsi_proc_entry *e;
int ret;

if (!sht->show_info)
return 0;

mutex_lock(&global_host_template_mutex);
if (!sht->present++) {
sht->proc_dir = proc_mkdir(sht->proc_name, proc_scsi);
if (!sht->proc_dir) {
printk(KERN_ERR "%s: proc_mkdir failed for %s\n",
__func__, sht->proc_name);
e = __scsi_lookup_proc_entry(sht);
if (!e) {
e = kzalloc(sizeof(*e), GFP_KERNEL);
if (!e) {
ret = -ENOMEM;
goto unlock;
}
}
if (e->present++)
goto success;
e->proc_dir = proc_mkdir(sht->proc_name, proc_scsi);
if (!e->proc_dir) {
printk(KERN_ERR "%s: proc_mkdir failed for %s\n", __func__,
sht->proc_name);
ret = -ENOMEM;
goto unlock;
}
e->sht = sht;
list_add_tail(&e->entry, &scsi_proc_list);
success:
e = NULL;
ret = 0;
unlock:
mutex_unlock(&global_host_template_mutex);

kfree(e);
return ret;
}

/**
* scsi_proc_hostdir_rm - remove directory in /proc for a scsi host
* @sht: owner of directory
*/
void scsi_proc_hostdir_rm(struct scsi_host_template *sht)
void scsi_proc_hostdir_rm(const struct scsi_host_template *sht)
{
struct scsi_proc_entry *e;

if (!sht->show_info)
return;

mutex_lock(&global_host_template_mutex);
if (!--sht->present && sht->proc_dir) {
e = __scsi_lookup_proc_entry(sht);
if (e && !--e->present) {
remove_proc_entry(sht->proc_name, proc_scsi);
sht->proc_dir = NULL;
list_del(&e->entry);
kfree(e);
}
mutex_unlock(&global_host_template_mutex);
}
Expand All @@ -153,20 +217,29 @@ void scsi_proc_hostdir_rm(struct scsi_host_template *sht)
*/
void scsi_proc_host_add(struct Scsi_Host *shost)
{
struct scsi_host_template *sht = shost->hostt;
const struct scsi_host_template *sht = shost->hostt;
struct scsi_proc_entry *e;
struct proc_dir_entry *p;
char name[10];

if (!sht->proc_dir)
if (!sht->show_info)
return;

e = scsi_lookup_proc_entry(sht);
if (!e)
goto err;

sprintf(name,"%d", shost->host_no);
p = proc_create_data(name, S_IRUGO | S_IWUSR,
sht->proc_dir, &proc_scsi_ops, shost);
p = proc_create_data(name, S_IRUGO | S_IWUSR, e->proc_dir,
&proc_scsi_ops, shost);
if (!p)
printk(KERN_ERR "%s: Failed to register host %d in"
"%s\n", __func__, shost->host_no,
sht->proc_name);
goto err;
return;

err:
shost_printk(KERN_ERR, shost,
"%s: Failed to register host (%s failed)\n", __func__,
e ? "proc_create_data()" : "scsi_proc_hostdir_add()");
}

/**
Expand All @@ -175,13 +248,19 @@ void scsi_proc_host_add(struct Scsi_Host *shost)
*/
void scsi_proc_host_rm(struct Scsi_Host *shost)
{
const struct scsi_host_template *sht = shost->hostt;
struct scsi_proc_entry *e;
char name[10];

if (!shost->hostt->proc_dir)
if (!sht->show_info)
return;

e = scsi_lookup_proc_entry(sht);
if (!e)
return;

sprintf(name,"%d", shost->host_no);
remove_proc_entry(name, shost->hostt->proc_dir);
remove_proc_entry(name, e->proc_dir);
}
/**
* proc_print_scsidevice - return data about this host
Expand Down
12 changes: 0 additions & 12 deletions include/scsi/scsi_host.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -357,12 +357,6 @@ struct scsi_host_template {
*/
const char *proc_name;

/*
* Used to store the procfs directory if a driver implements the
* show_info method.
*/
struct proc_dir_entry *proc_dir;

/*
* This determines if we will use a non-interrupt driven
* or an interrupt driven scheme. It is set to the maximum number
Expand Down Expand Up @@ -423,12 +417,6 @@ struct scsi_host_template {
*/
short cmd_per_lun;

/*
* present contains counter indicating how many boards of this
* type were found when we did the scan.
*/
unsigned char present;

/* If use block layer to manage tags, this is tag allocation policy */
int tag_alloc_policy;

Expand Down

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