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Fri, 27 Jun 2025 00:18:52 -0700 (PDT) Received: from tigerii.tok.corp.google.com ([2401:fa00:8f:203:de1c:e88f:de93:cd95]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-23acb2f1814sm9316095ad.57.2025.06.27.00.18.50 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 27 Jun 2025 00:18:51 -0700 (PDT) From: Sergey Senozhatsky To: Jens Axboe Cc: Minchan Kim , Rahul Kumar , linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, Sergey Senozhatsky Subject: [PATCH] zram: pass buffer offset to zcomp_available_show() Date: Fri, 27 Jun 2025 16:18:21 +0900 Message-ID: <20250627071840.1394242-1-senozhatsky@chromium.org> X-Mailer: git-send-email 2.50.0.727.gbf7dc18ff4-goog In-Reply-To: <20250627035256.1120740-1-rk0006818@gmail.com> References: <20250627035256.1120740-1-rk0006818@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" In most cases zcomp_available_show() is the only emitting function that is called from sysfs read() handler, so it assumes that there is a whole PAGE_SIZE buffer to work with. There is an exception, however: recomp_algorithm_show(). In recomp_algorithm_show() we prepend the buffer with priority number before we pass it to zcomp_available_show(), so it cannot assume PAGE_SIZE anymore and must take recomp_algorithm_show() modifications into consideration. Therefore we need to pass buffer offset to zcomp_available_show(). Also convert it to use sysfs_emit_at(), to stay aligned with the rest of zram's sysfs read() handlers. On practice we are never even close to using the whole PAGE_SIZE buffer, so that's not a critical bug, but still. Signed-off-by: Sergey Senozhatsky --- drivers/block/zram/zcomp.c | 15 +++++++-------- drivers/block/zram/zcomp.h | 2 +- drivers/block/zram/zram_drv.c | 9 +++++---- 3 files changed, 13 insertions(+), 13 deletions(-) diff --git a/drivers/block/zram/zcomp.c b/drivers/block/zram/zcomp.c index d26a58c67e95..b1bd1daa0060 100644 --- a/drivers/block/zram/zcomp.c +++ b/drivers/block/zram/zcomp.c @@ -8,6 +8,7 @@ #include #include #include +#include =20 #include "zcomp.h" =20 @@ -89,23 +90,21 @@ bool zcomp_available_algorithm(const char *comp) } =20 /* show available compressors */ -ssize_t zcomp_available_show(const char *comp, char *buf) +ssize_t zcomp_available_show(const char *comp, char *buf, ssize_t at) { - ssize_t sz =3D 0; int i; =20 for (i =3D 0; i < ARRAY_SIZE(backends) - 1; i++) { if (!strcmp(comp, backends[i]->name)) { - sz +=3D scnprintf(buf + sz, PAGE_SIZE - sz - 2, - "[%s] ", backends[i]->name); + at +=3D sysfs_emit_at(buf, at, "[%s] ", + backends[i]->name); } else { - sz +=3D scnprintf(buf + sz, PAGE_SIZE - sz - 2, - "%s ", backends[i]->name); + at +=3D sysfs_emit_at(buf, at, "%s ", backends[i]->name); } } =20 - sz +=3D scnprintf(buf + sz, PAGE_SIZE - sz, "\n"); - return sz; + at +=3D sysfs_emit_at(buf, at, "\n"); + return at; } =20 struct zcomp_strm *zcomp_stream_get(struct zcomp *comp) diff --git a/drivers/block/zram/zcomp.h b/drivers/block/zram/zcomp.h index 4acffe671a5e..eacfd3f7d61d 100644 --- a/drivers/block/zram/zcomp.h +++ b/drivers/block/zram/zcomp.h @@ -79,7 +79,7 @@ struct zcomp { =20 int zcomp_cpu_up_prepare(unsigned int cpu, struct hlist_node *node); int zcomp_cpu_dead(unsigned int cpu, struct hlist_node *node); -ssize_t zcomp_available_show(const char *comp, char *buf); +ssize_t zcomp_available_show(const char *comp, char *buf, ssize_t at); bool zcomp_available_algorithm(const char *comp); =20 struct zcomp *zcomp_create(const char *alg, struct zcomp_params *params); diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c index 385aaaa2531b..8acad3cc6e6e 100644 --- a/drivers/block/zram/zram_drv.c +++ b/drivers/block/zram/zram_drv.c @@ -1225,12 +1225,13 @@ static void comp_algorithm_set(struct zram *zram, u= 32 prio, const char *alg) zram->comp_algs[prio] =3D alg; } =20 -static ssize_t __comp_algorithm_show(struct zram *zram, u32 prio, char *bu= f) +static ssize_t __comp_algorithm_show(struct zram *zram, u32 prio, + char *buf, ssize_t at) { ssize_t sz; =20 down_read(&zram->init_lock); - sz =3D zcomp_available_show(zram->comp_algs[prio], buf); + sz =3D zcomp_available_show(zram->comp_algs[prio], buf, at); up_read(&zram->init_lock); =20 return sz; @@ -1387,7 +1388,7 @@ static ssize_t comp_algorithm_show(struct device *dev, { struct zram *zram =3D dev_to_zram(dev); =20 - return __comp_algorithm_show(zram, ZRAM_PRIMARY_COMP, buf); + return __comp_algorithm_show(zram, ZRAM_PRIMARY_COMP, buf, 0); } =20 static ssize_t comp_algorithm_store(struct device *dev, @@ -1416,7 +1417,7 @@ static ssize_t recomp_algorithm_show(struct device *d= ev, continue; =20 sz +=3D sysfs_emit_at(buf, sz, "#%d: ", prio); - sz +=3D __comp_algorithm_show(zram, prio, buf + sz); + sz +=3D __comp_algorithm_show(zram, prio, buf, sz); } =20 return sz; --=20 2.50.0.727.gbf7dc18ff4-goog