[PATCH RFC 0/3] fs: tftp: don't use cached dentries

[PATCH RFC 0/3] fs: tftp: don't use cached dentries

[Ahmad Fatoum]

I often mistype the name of files I place into the TFTP server's root
directory. When barebox does a TFTP lookup for the correct file name and
doesn't find it, it refuses to look it up again. I'd argue the better
user experience for TFTP in particular would be to not use the dcache
altogether. Not sure if other networked file systems should follow suit,
as staleness means faster acceses, but lets do this for TFTP now.

The file is still placed and invalidated from the cache though, but
compared to the network access before, it's negligible overhead.

Ahmad Fatoum (3):
  fs: tftp: remove duplicate header
  fs: provide no_revalidate_d_ops for network file systems
  fs: tftp: don't maintain tftp dentries in dcache

 fs/fs.c                | 9 +++++++++
 fs/tftp.c              | 2 +-
 include/linux/dcache.h | 2 ++
 3 files changed, 12 insertions(+), 1 deletion(-)

-- 
2.20.1


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[PATCH RFC 1/3] fs: tftp: remove duplicate header

[Ahmad Fatoum]

<fs.h> is included again a few lines prior. Delete it here.

Signed-off-by: Ahmad Fatoum <ahmad@a3f.at>
---
 fs/tftp.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/fs/tftp.c b/fs/tftp.c
index 43293272d7e9..54dcba272fb8 100644
--- a/fs/tftp.c
+++ b/fs/tftp.c
@@ -29,7 +29,6 @@
 #include <libgen.h>
 #include <fcntl.h>
 #include <getopt.h>
-#include <fs.h>
 #include <init.h>
 #include <linux/stat.h>
 #include <linux/err.h>
-- 
2.20.1


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[PATCH RFC 2/3] fs: provide no_revalidate_d_ops for network file systems

[Ahmad Fatoum]

Networked file systems may wish to forego dentry caching altogether, so
every lookup goes over the network and stale data is avoided.
Provide a no_revalidate_d_ops helper object that does this.

Signed-off-by: Ahmad Fatoum <ahmad@a3f.at>
---
 fs/fs.c                | 9 +++++++++
 include/linux/dcache.h | 2 ++
 2 files changed, 11 insertions(+)

diff --git a/fs/fs.c b/fs/fs.c
index c6cb49996ec5..dda19db91341 100644
--- a/fs/fs.c
+++ b/fs/fs.c
@@ -1262,6 +1262,15 @@ static void d_invalidate(struct dentry *dentry)
 {
 }
 
+static int d_no_revalidate(struct dentry *dir, unsigned int flags)
+{
+	return 0;
+}
+
+const struct dentry_operations no_revalidate_d_ops = {
+	.d_revalidate = d_no_revalidate,
+};
+
 static inline int d_revalidate(struct dentry *dentry, unsigned int flags)
 {
 	if (unlikely(dentry->d_flags & DCACHE_OP_REVALIDATE))
diff --git a/include/linux/dcache.h b/include/linux/dcache.h
index 1581ddc701d3..a9619422013e 100644
--- a/include/linux/dcache.h
+++ b/include/linux/dcache.h
@@ -185,4 +185,6 @@ static inline struct inode *d_inode(const struct dentry *dentry)
 
 char *dpath(struct dentry *dentry, struct dentry *root);
 
+extern const struct dentry_operations no_revalidate_d_ops;
+
 #endif	/* __LINUX_DCACHE_H */
-- 
2.20.1


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[PATCH RFC 3/3] fs: tftp: don't maintain tftp dentries in dcache

[Ahmad Fatoum]

Currently a negative dentry is cached whenever a non-existing file was
looked up over TFTP. Short of a barebox reset, there is no way to
invalidate that dentry, so barebox retries the look up.

Fix this by always reporting TFTP dentries as invalid in the d_revalidate
callback.

Signed-off-by: Ahmad Fatoum <ahmad@a3f.at>
---
 fs/tftp.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/fs/tftp.c b/fs/tftp.c
index 54dcba272fb8..1f36c56511ac 100644
--- a/fs/tftp.c
+++ b/fs/tftp.c
@@ -715,6 +715,7 @@ static int tftp_probe(struct device_d *dev)
 	}
 
 	sb->s_op = &tftp_ops;
+	sb->s_d_op = &no_revalidate_d_ops;
 
 	inode = tftp_get_inode(sb, NULL, S_IFDIR);
 	sb->s_root = d_make_root(inode);
-- 
2.20.1


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Re: [PATCH RFC 0/3] fs: tftp: don't use cached dentries

[Sascha Hauer]

On Thu, Aug 22, 2019 at 08:50:59AM +0200, Ahmad Fatoum wrote:
> I often mistype the name of files I place into the TFTP server's root
> directory. When barebox does a TFTP lookup for the correct file name and
> doesn't find it, it refuses to look it up again. I'd argue the better
> user experience for TFTP in particular would be to not use the dcache
> altogether. Not sure if other networked file systems should follow suit,
> as staleness means faster acceses, but lets do this for TFTP now.
> 
> The file is still placed and invalidated from the cache though, but
> compared to the network access before, it's negligible overhead.
> 
> Ahmad Fatoum (3):
>   fs: tftp: remove duplicate header
>   fs: provide no_revalidate_d_ops for network file systems
>   fs: tftp: don't maintain tftp dentries in dcache

Applied, thanks. I stumbled upon this behaviour myself aswell.

Sascha

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